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, Miiller 

 proposes to apply the name of Vivipara acotyledona^ 

 answering to the more familiar term of Ovo-vlvipa- 

 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 Scyllhim of the Sharks, 

 and the Raia proper, and Chimera among the Rays, 

 have a fine homy 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 

 horns. 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 pl»^« invariably in water. 



