20 < oMl'AUATIVK AJffATOMY. 



were much more abundant in Amphibians of former times; those 

 of the < 'arboniferous and Trias (Stegocephala, Labyrinthodonta) 



were richly provided with them. 



F. >r a I'lirlluT ivl'm-nr.- 1.. llir rin;_<-likr M-uti-.- and scales fumnl in ( ';irili;m>, 



tllr iv.-i'lt T !.- ivfi-nvtl In tin- rh;i]iti-r nil tin- (liTlnal ,-krli'to]], allil it is only 



necessary 1<> stair ln-iv ilial tin- rin^s ai-i-uratrly ri.nv.-iiniiil in numlu-r with 

 tin- \ rrtrl'rav a vrry ran- occurrence. The same is true of certain Ampliis- 

 ii;i_-nian< (e.g. lilnmi.* cinen //.-). 



Reptilia. In contrast to the skin of Amphibians, that 

 of Reptiles is very deficient in glands. In Lizards, a series 

 if " femoral glands" occur alon^ the ventral side of the thigh, 

 tli-' seeretinn from \vliicli, as it passes out of the a pertures, hardens 

 so as to form a series of pnpillu; or warts, which ap])ear to serve as 

 clasping organs during copulation. In Ampbisbsenians integu- 

 mentary glands are also present: they lie anteriorly to the cloaca. 

 and open into the "pre-anal pores." 



The characteristic peculiarity of the skin of Reptiles 

 is its capacity of producing scales, warts, prickles, shields 

 {e.g. the " tortoises!) ell" of Chelonians), claws, rattles (of Rattle- 

 snake), and suchlike structures. 



All these integumentary organs, as already mentioned (p. 1C), 

 are to be included in tin- same category as the feathers of 

 Birds and the hairs of Mammals: that is, all arise at lirst by a 

 proliferation of the epidermic cells, a portion <>f the dermal tissue 

 taking part in their formation later on. Certain special differences 

 are, however, always to be observed in the development of these 

 different structures, as will be mentioned presently. 



As in Amphibia, calcifications or ossifications may occur in 

 the derma. The horny layer of the epidermis may be either 

 periodically cast off entire (Snakes), or in shreds from time to 

 time: it is renewed from the Malpighian layer. Pigment-cells 

 also occur, rendering possible in many eases a change of colour 

 (e.g. Chameleon 



Birds. IJinls possess a thinner derma than do any other 



Vertebrates, and it is not \er\ plentifully supplied with blood- 



JSels, although, as will lie mentioned in another chapter, sensory 



organ> (tactile corpuscles; are abundant. In the deeper layers 



theivi> a stroiivjv developed network of muscle-til >res, \\ hich a iv 



inserted into the feather-sacs, and serve to ereci the feathers. 



Tin- feathers, arranged in so-called " teat hei-t racts " (jiteryla?) 

 separated 1>\ naked regions (apteria), 1'orm the nm^t marked 

 peculiarity of the body of P>irds, and their development IS very 

 in>t 1'iict i\ e. In the region \\heiv a feather is to lie formed, the 

 dermal tissue becomes raised up to\\anls the ectoderm i Fig. 1 :?. A. 



I'n. >'<, N.)/';. and tlni's -ives rise to a papilla (J']>\ As this papilla 

 grows out to form an elon-ated com' with a pointed ape\, the 



feather-germ Fi-. 1_ I'. /V\'i. its base sinks^pradually deeper and 



