Aristotle's biology 



packed full of a multitude of facts, in no one 

 of which did Johannes Miiller discover a flaw. 

 The subject is technical, but the gist of the 

 matter is this: that among the Selachians (as, 

 after Aristotle, we still sometimes call them) 

 there are many diversities in the structure of 

 the parts in question, and several distinct 

 modes in which the young are brought forth 

 and matured. For in many kinds an egg is 

 laid, which eggs, by the way, Aristotle de- 

 scribes with great minuteness. Other kinds 

 do not lay eggs, but bring forth their young 

 alive, and these include the Torpedo and 

 numerous sharks or dogfish. The egg-shell is 

 in these cases very thin, and breaks before the 

 birth of the young. But among them there are 

 a couple of sharks, of which one species was 

 within Aristotle's reach, where a very curious 

 thing happens. Through the delicate mem- 

 brane, which is all that is left of the egg-shell, 

 the great yolk-sac of the embryo becomes con- 

 nected with the parental tissues, which infold 

 and interweave with it; and by means of this 

 temporary union the blood of the parent be- 

 comes the medium of nourishment for the 

 young. And the whole arrangement is physio- 

 logically identical with what obtains in the 



[57] 



