2,2 AMPHIBIA CHAP. 



Amphibia in rme piece. In the Urodelu it generally breaks 

 loose around the mouth, and the animal slips out of the delicate, 

 transparent, colourless " shirt," which during this process of 

 ecdysis or moulting becomes inverted. In the Anura it mostly 

 breaks along the middle line of the back, the creature struggles 

 out t>f it, pokes it into its mouth, and swallows it. Urodela 

 also eat this skin. As a rule the first ecdysis takes place 

 towards the end of the metamorphosis, preparatory to terrestrial 

 life. So long as the animal grows rapidly, the skin has to be 

 shed frequently, since this corneous layer is practically dead and 

 imyielding. Adult terrestrial Urodela do not seem to moult 

 often, mostly only when they take to the water in the breeding- 

 season. Anura, on the other hand, moult often on land, at least 

 every few months. Tlie surface of the new skin is then quite 

 moist and slimy, but it soon dries and hardens. 



The Malpighian stratum consists of several layers, thickest 

 ill tlie Perennibranchiata ; in them it contains mucous cells 

 tliroughout life, in others such slime-cells are restricted to larval 

 life. Later, regular slime-glands are developed, which open 

 on tlie surface. They are very numerous, and more evenly 

 distributed, over most parts of the body, than the specific or 

 poison-glands, which are restricted to certain parts, often form- 

 ing large clusters, especially on the sides of the body. They 

 reach their greatest development in the " parotoid glands " of 

 the Anura. Botii kinds of glands are furnished with smooth 

 muscle-fibres, which are said to ai'ise from the basal membrane 

 miderlying and forming part of the Malpighian layer ; these 

 muscle-cells extend later downwards into the coriuni. For the 

 a(;tion of the poison, see p. 37. 



The stratum corneum is mostly thin, but on many parts of 

 the body, especially in Anura, the epidermal cells proliferate and 

 form hard spikes or other rugosities, generally stained dark brown. 

 With these may be grouped the nuptial excrescences so frequent in 

 the Anura, especially on the rudiment of the thumb, and on the 

 under surface of the joints of the fingers and toes. In many 

 Anura, less frequently in tlie IT^.^dela, the tips of the fingers and 

 toes are encased in thicker horny sheaths, producing claws or 

 nails. They are best develojied among newts in Onychodmtylus, 

 among the Anura in Xeno}ms and Ili/mmochirus. The horny 

 covering of the metatarsal tubercles reaches its greatest size in 



