u 



COMPARATIVE ANATOMY 



ment of Fishes, but apart from Protopterus (see above) there are a 

 number of exceptions to this rule. 



In male Elasmobranchs there is a large c/landtda pterygopodii (gland 

 of the clasper) at the base of each pelvic iin : it arises as a tube-like invagin- 

 ation of the skin, and is in relation with the copulatory organs. Poison-glands 

 are found amongst the Teleostei. Thus in the Weever (Trachinus) there 

 is a series of poison-glands lying on either side of the bases of the spines of 

 the dorsal fin and operculum. In Thalassophryne the operculum is provided 

 with a hollow spine, at the base of which a poison-gland is situated, and in 

 Synanceia there is also a series of glands at the bases of the grooved dorsal 

 spines. Poison organs are also present in Soorpsena and others ; but in many 

 cases in which such organs have been described a more detailed histological 

 examination is desirable. The 2}hosphoresce'itt and eye-like orrjans present in 

 the integument of some Fishes (Scopelidse, Chauliodus, &o.) are probably 

 to be looked upon as modified glands. 



In Lepidosiren, apparently in the male only, the integument of the 

 pelvic fins is provided with numerous (? erectile) villi. 



Pigment-cells, which are under the influence of the nervous 

 system and are able to cause a change of colour, are present some- 

 times in both layers of the integument, sometimes in the epidermis 

 only. The colouration is sometimes protective (e.ff. Flat-fishes) and 

 sometimes se.xual (e.g. Stickleback). 



The boni/ scales of Fishes lie in connective-tissue pouches of 

 the dermis and are formed as ossifications of the latter. In 

 Teleosts and Dipnoans they are covered by the epidermis through- 

 out life ; in Ganoids and Elasmobranchs this is only the case in the 

 larva. In Teleosts the parts of the epidermis covering the ex- 

 ternally visible portions of the scales become cornified. (For- 

 further details compare p. 30). 



Amphibia. — The epidermis of Amphibian larvse is for a short 

 period ciliated. In the adult, it may be said in general that the 



Fig. 11.— Skin of Larva of S.^lamaxder {Sa/amaiidra macidom). 



Ep, epidermis; Co, dermi.s ; a, stratum corneura ; fc, stratiun ilalpighii ; LZ,. 

 Leydig's cells ; C.S', striated border. 



integument of Amphibians is intermediate in structure between 

 that of Fishes and Keptiles. 



The epidermis of those larvte which live in the water consists 

 of two sharply differentiated layers. The outer layer is usually 

 made up of flat cells with a striated cuticular border on their 

 free edge (Fig. 11), like that occurring amongst Fishes : the inner- 



