420 TEGUMENTARY ORGANS 



secretion of the axillary sudoriparous glands in man being an 

 essentially sebaceous substance. The sudoriparous glands are 

 cylindrical ccecal tubes varying, in man, from -j-J-jj- to yJo- 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 muscles, and the whole 

 is coated, like the deep surface 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 

 frequently so thick that they possess no cavity at all. The thick- 

 walled glands are met with in man in the axilla, scrotum, anal region, 

 &c. ; while those of the rest of the body are almost 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 ox and dog they are straight 

 and simple. In the ox they have rounded, dilated 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 Accipenser and Polypterus 

 the substance of the scales is composed of ordinary bone whose 

 superficial layer is only denser than the rest, and exhibits a local 

 development of fine branching tubuli ; but in other fishes, two, if not 

 three, distinct layers are usually distinguishable 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 



