62 INTRODUCTION. 



to their use. To those viviparous animals in which 

 the ova are thus situated, having no connexion by 

 means of vascular cotyledons, or a placenta, Muller 

 proposes to apply the name of Vivipara acotyledona, 

 answering to the more familiar term of Ovo-vivipa- 

 rous. Thirdly, The last division of animals is that 

 in which a connexion with the parent, destined for 

 the conferring and assumption of nutriment, exists : 

 these he designates by the name of Vivipara Coty- 

 lophora. 



The greater number of animals, invertebrate as 

 well as vertebrate, are Oviparous, — the oviparous 

 vertebrates comprehending the majority of fishes, 

 reptiles, and birds. The exceptions in the case of 

 fishes, with some isolated ones presently to be men- 

 tioned, are found chiefly in the plagiostomatous, — 

 flat-mouthed fishes, — the Sharks and Rays, which, 

 generally speaking, are viviparous. Such of them 

 as are not, as the groups Scyllium of the Sharks, 

 and the Rata proper, and Chimera among the Rays, 

 have a fine horny shell, well known under the fami- 

 liar names of Mermaid's, Sailors, or Sea-purses, 

 usually of a flat form, oblong in the sharks, often 

 yellow and transparent; and square in the rays, 

 with the four angles prolonged and pointed, like 

 hoins. The gland which is destined for the forma- 

 tion of this shell in these animals is remarkably 

 developed. The ova of oviparous animals when 

 deposited, in some cases undergo their further de- 

 velopement in water, in other cases on land ; those 

 of fishes taking place invariably in water. 



