Sudoriparous glands.— These glands, like those just described, are, as Gurlt pointed out, simple, elongated processes of the deep layer of the ecderon, differing from the sebaceous glands chiefly in producing a clear fluid, instead of a fatty secretion. As Kolliker has shown, however, no line of demarcation is to be drawn on this ground, the secretion of the axillary sudoriparous glands in man being an essentially sebaceous substance. The sudoriparous glands are cylindrical ccecal tubes varying, in man, froni Th to ,4-6 of an inch in diameter, whose walls are either thick or thin. In the former case they consist of a simple ecderonic cellular coat, contained within a prolonged sheath, formed by the uppermost layer of the enderon, and, like it, composed of a homogeneous or indistinctly fibrillated periplast, with imbedded endoplasts. Outside this, or rather forming part of it, is a layer of longitudinally-disposed smooth mus cles, and the whole is coated, like the deep sur face of the rest of the enderon, by a more or less distinct layer of connective tissue. In the thin-coated glands the muscular layer is absent, but the cellular ecderonic coat is fre quently so thick that they possess no cavity at all. The thick-walled glands are met with in man in the axilla, scrotum, anal region, Sze. ; while those of the rest of the body are al most entirely of the thin-walled description. The glands terminate superiorly in undu lating canals, which reach the surface of the enderon, and are continued to that of the ecderon by oblique channels excavated in its substance between its cells. Inferiorly, they form close coils, which lie in the subcutaneous areolar tissue, and receive twigs from the vessels in their neighbourhood.
In the other Mammalia, the general structure of the sudoriparous glands is as in man. In the sheep, according to Gurlt,they present the same coiled arrangement, while in the GC and dog they are straight and simple. In the ox they have rounded, d.lated extremities, and are everywhere similar in shape and size. On the hairy parts of the body of the dog, they are small simple cceca, which are very difficult to discover ; while on the ball of the foot of this animal they are very large and resemble those of man. Very large sudoriparous glands have likewise been observed upon the horse's prepuce.
Scales of fishes.— In the Ganoid fishes Ac cipenser and Potypterus the substance of the scales is composed of ordinary bone whose superficial layer is only denser than the rest, and exhibits a local developement of fine branching tuba ; but in other fishes, two, if not three, distinct layers are usually distin guishable in the scales.
In many Plagiostomes, for instance, the placoid scales have the same composition as the teeth, consisting of a superficial layer of nearly structureless dense " enamel," or as Prof. Williamson more conveniently terms it, " Ganoin," while the deeper substance is composed of a tissue in every respect similar to dentine, whose innermost portion in some cases passes into true bone, — an addition which might be compared to that of the cement in the teeth. Leydig, indeed, has shown that the resemblances between the scales and the teeth of Placoid fish extend even to their mode of developement. If the pulp contained in the central cavity of the spine-like scale of a Rata clavata be pulled out, globular calcareous masses of -rdio , of an inch and upwards in diameter, and either solitary or adhering together in masses, will be found to be attached to its surface. " These
globules are exactly analogous to the dentine globules described by Czermak, which in human teeth afford the formative material for the n3atrix of the dentine. What, however, ap peared to me especially worthy of notice was the circumstance, that the most distinct and beautifully branched canals, having exactly the same appearance as those in the substance of the spine, were already visible in these isolated calcareous bodies, and on carefully examining the fine procesaes of the canals, no doubt could exist that they were only interspaces or gaps. On carefully adjusting the focus, in fact, it was obvious that one of these large calcareous globules is itself only an agglomeration of many smaller globules, and it could be observed that the gaps left between the latter became the fine processes of the tubules. From these facts, I believe that the correct mode of conceiving the growth of the substance of the spine is, to suppose that the calcareous matter is excreted from the vessels of the pulp, and then in all probability combined with organic matter, runs into smaller masses ; these unite together into larger ones, and become applied to the inner surface of the central cavity, coalescing, and thus adding to the thickness of the spine. Betw een the calcareous globules, however, canalicular gaps or tubules' remain, which form a connected network and communicate with those branched cavities which already exist in the spine.
The scales of the Sharks and the dermal spines of the Rays, then, (and I would draw particular attention to this result,) are per fectly identical in structure with the teeth, even to the absence of nerves in the pulp, and must be united in the same structural group. I have already (On the Skin of Fresh water Fishes, Zeitschrift filr Wiss. Zool. B. iii. H. 4.) pointed out the close affinity be tween the scales of a number of osseous fishes and their teeth : and scales likewise present globules of calcareous matter, which become fused together to form the homo geneous substance of the scale. A process, corresponding with that which occurs at the surface of the pulp in the teeth and cutaneous spines, here takes place from the surface of the sac of the scale (Schuppentasche). The scales of osseous fishes, the spines of the Rays, and the scales of the Sharks, therefore, all belong to the series of dental structures, which in no respect interferes with the en trance of true bony tissue (like the "cement " in the higher animals) into their composition, as we find to be the ca.se in the scales of the Ganoids (Milller), and in the truly bony semi canals which are attached to the scales of the lateral lines of many fishes." * For the details of the various modes in which Ganoin, true osseous tissue, and those va rieties of tubular, more or less dentine-like tissues, to which Prof. Williamso# has given the names of " Lepidine and Kosmine," are combined together in the scales of Ganoid and Placoid fish, I must refer to that gentle man's memoirs, already so often cited.