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the pulp-cavity. The dentine will, when cut, break up into small fragments, and from the edges of these the fibrils may be seen extending. Sometimes a small portion of the pulp will be found adherent, in which case the fibrils may be seen to extend from that tissue into the dentine. The fibrils may be shown in a more striking manner by decalcifying a section, and then, when it is placed upon a slide, tearing the specimen across the direction of the tubes. By this manipulation, the fibrils will be dragged out from one fragment, and will be seen projecting from the edge of the other.

The fibrils, when isolated and examined with a high power, without the presence of a reagent, show some indications of tubularity, but not with sufficient distinctness to enable the author to determine whether they are tubes or solid bodies. Their appearance

is

very like that of the ultimate fibrils of spinal nerves, and they possess a character in common with these, in the presence of minute globules of dense transparent matter exuded from the broken ends, and sometimes from the surface of the fibril. It is not easy to determine in what manner the fibrils commence in the pulp. In some preparations they appear to be connected with cells situated a short distance within the pulp, in others they may be traced to a greater depth, where they are lost in the tissue of the pulp, and may possibly be connected with the nerves, which in this part are very abundant. But in the absence of exact knowledge as to the manner in which the dentinal fibrils are related to the elements of the pulp, the author considers that there is sufficient evidence to warrant the conclusion that they are organs of sensation, the distribution of which through the substance of the dentine endows that tissue with its sensibility.

This conclusion is borne out by the occurrence of the following conditions. If a fragment of enamel be broken from the surface of the dentine, the exposed portion of the latter tissue is highly sensitive to the contact of foreign bodies; but if the force producing the injury be sufficient to rupture the nerves and vessels where they enter the root of the tooth, the dentine loses its capability of feeling pain. Again, if the dentine be exposed by the gradual wearing away of the enamel by mastication, the surface evinces no sensibility, a circumstance accounted for by the fact that the dentinal tubes have become consolidated, either at the surface exposed, or at some point between the surface and the pulp-cavity. Diseased teeth furnish

further evidence in favour of the foregoing views. If a carious tooth, in which the disease has advanced but slowly, and the carious portion is dark in colour and tolerably firm in consistence, be examined, it will be found that the dentinal fibrils have become calcified, and in a favourable section they may be seen projecting from the edge of the specimen, or lying broken in short lengths in the tubes. On removing the diseased part of the tooth in such a case, no pain is experienced until the instrument reaches the healthy dentine. Supposing, however, the disease to have been rapid in its progress, the carious tissue will be light in colour, and, as compared with the preceding example, soft in consistence. The removal of the affected part in this case is frequently attended with considerable pain. . Examination will then show that the dentinal fibrils have not been consolidated, but may be found here and there extending into the softened tissue without having suffered any appreciable alteration of appearance.

Daily experience shows that a tooth may remain useful for a long time after the pulp, and consequently the dentinal fibrils, have been destroyed. If, however, a tooth which has been so circumstanced be examined, it will be found that one of two actions has been set up. Either additional cementum will have been developed upon the surface of the fang, or its bulk will have become diminished by absorption. Similar conditions supervene when the crown of a tooth has been lost by caries.

In old persons we find the teeth are lost without apparent disease in the dental tissues. The teeth become loose and fall out, the roots being in such cases translucent like horn. This condition is the result of consolidation of the dentinal fibrils, and is followed by absorption of the cementum and dentine. Cases may be found in which the whole of the fang has been absorbed, but reduction to two-thirds or half of the normal bulk is very common.

The concurrence of the foregoing changes in the sensibility of the tooth, with the destruction or consolidation of the dentinal fibrils, will, the author considers, justify the conclusion, that the dentinal fibrils, in a state of integrity, are necessary to the normal condition of dentine.

II. “On the Structure and Development of the Cysticercus Cel

lulosæ, as found in the Pig." By GEORGE RAINEY, Esq., Lecturer, and Demonstrator of Practical and Microscopical Anatomy at St. Thomas's Hospital. Communicated by ROBERT D. THOMSON, M.D., F.R.S. Received February 15, 1856.

The present communication is an enlarged and revised version, illustrated with figures, of a paper by the author, bearing the same title, which was read on the 13th December 1855, and was subsequently, by permission, withdrawn. An abstract will be found in the Proceedings' under the date referred to.

III. A paper was in part read, entitled “On the Direcious

Character of the Rotifera.By Philip HENRY GOSSE,
Esq. Communicated by Thomas Bell, Esq., F.R.S.,
Pres.L.S. Received February 19, 1856.

The Society then adjourned over the Easter holidays, to Thursday, April 3.

April 3, 1856.

Sir PHILIP DE MALPAS GREY EGERTON, Bart., V.P.,

in the Chair.

The reading of Mr. Gosse's paper, “On the Diæcious Character of the Rotifera,” was resumed and concluded.

(Abstract.) Professor Ehrenberg, in his descriptions of this class of animals, assumed them to be in every case hermaphrodite. His conclusions remained unchallenged till 1848, when Mr. Brightwell discovered the separate sexes of Asplanchna Brightwellii. The author of this memoir soon afterwards discovered a second species of the same genus (4. priodonta) with a like dicecious character ; and more recently Dr. Leydig has added a third (4. Sieboldii), which does not differ in this respect from its congeners.

Dr. Leydig plausibly conjectures that Enteroplea of Ehrenberg is the male sex of Hydatina, that Notommata granularis is the male of N. Brachionus, and that Diglena granularis of Weisse is the male of D. Catellina.

The author of the present memoir has ascertained from his own observations that the sexes are separate also in Brachionus Pala, B. rubens, B. amphiceros, B. angularis, B. Bakeri, B. Dorcas, B. Mülleri, Synchæta tremula, Polyarthra platyptera, Sacculus viridis, and Melicerta ringens. The males of these species, which are here described in detail, differ so greatly from the females in form, size, and structure, that they could not have been supposed to belong to the same genera, or even families, if their parentage had not been distinctly determined.

One of the most remarkable characters of male Rotifera is the absolute and universal atrophy of the digestive system. No mastax, jaws, csophagus, stomach, or intestines occur in any example of any species. Another peculiarity is the great disparity between the sexes. In

every

observed case the male is inferior in size and in organization to the female.

The muscular system is well developed in the males of Hydatina, Asplanchna, and Brach. Mülleri. The frontal cilia are in general greatly developed in this sex, the result of which is seen in the energy and rapidity of its locomotion. In most instances the great occipital ganglion is distinct, with a red eye seated on it; and the latter is almost always present, even where the ganglion cannot be defined. The lateral convoluted threads appear in Hydatina, Asplanchna, and Brach. dorcas ; and in Aspl. Brightwellü they are accompanied by tremulous tags, and by a contractile bladder.

Irregular masses of opake substance are almost constantly present in male Rotifera. This substance Dr. Leydig considers a urinary concretion.

In all cases the abdominal cavity is occupied by a capacious spermsac, from which spermatozoa are forced out by pressure. The outlet of the sperm-sac is by a thick, protrusile, and retractile penis. In those species which possess a foot, the intromittent organ is soldered to its dorsal side, and is often so greatly developed that the foot itself appears as an appendage. The penis is protruded by eversion; and is then seen to be a thick column with the extremity truncate and ciliated. The sexual coitus has been witnessed by the author in several instances.

For a parallel to the curious facts thus established, the author considers we must look to the Crustacea. The Hectocotylus of certain Mollusca is scarcely an analogous case ; nor are those Entozoa in which the males are organically united to the females.

In the Crustacea, however, many examples occur of a sexual difference which may be compared with that of the subjects of this memoir. In the genera Bopyrus, Phryxus, and Ione, the males are notably smaller than the females, very diverse in form, and in some respects inferior in structure. In the Siphonostoma, “the males are extremely small, and do not in the least resemble the females" (Baird); though those of different genera bear a strong resemblance inter se, even where the females are very dissimilar. So low is their grade of organization, that Burmeister has attempted to prove the minute males to be embryonic forms. Finally, in the Cirripedia, Mr. Darwin has proved the existence of males in the genera Ibla and Scalpellum, which are very minute as compared with their females, excessively abnormal in form, and in some respects in an embryonic condition, though unquestionably mature, as shown by their spermatozoa. And, what is still more interesting, there is, in these male Cirripedia, “no vestige of a mouth, or masticatory organs, or stomach.” The same observer describes the internal structure as "a pulpy mass with numerous oil-globules ;” and the sperm-vesicle as "a pear-shaped bag at the very bottom of the sack-formed animal containing either pulpy matter, or a great mass of spermatozoa,” — terms which might have been employed in describing some of the male Brachioni.

In all these analogies, the author finds additional reasons for assigning to the Rotifera a zoological rank among the Articulata.

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