Aristotle 37 



' produce the egg in a perfect, others in an imperfect state, 

 but it is perfected outside the body ashas been stated of fish.' 1 



Yet though Aristotle regarded fish as an oviparous group, 

 he knew also of kinds of fish that were externally viviparous. 

 It is most interesting to observe, moreover, that he wa^ 

 acquainted with one particular instance among fish in which 

 matters were less simple and in which the development bore 

 an analogy to that of the mammalia, his true internal vivipara. 

 4 Some animals ', he says, ' are viviparous, others oviparous, others 

 vermiparous. Some are viviparous, such as man, the horse, the 

 seal and all other animals that are hair-coated, and, of marine 

 animals, the Cetaceans, as the dolphin, and the so-called 

 Selacbia? 2 



Aristotle tells us elsewhere that a species of these Selachia 

 which he calls galeos a name still used for the dog-fish by 

 Greek fishermen 6 has its eggs in betwixt the [two horns of 

 the] womb ; these eggs shift into each of the two horns of the 

 womb and descend, and the young develop with the navel- 

 string attached to the womb, so that, as the egg-substance gets 

 used up, the embryo is sustained to all appearances just as in 

 quadrupeds. The navel-string is ... attached as it were by a 

 sucker, and also to the centre of the embryo in the place where 

 the liver is situated. . . . Each embryo, as in the case of quadru- 

 peds, is provided with a chorion and separate membranes.' 3 



The remarkable anatomical relationship of the embryo uf 

 Galeus (Mustelus) laevis to its mother's womb was little noticed 

 by naturalists until the whole matter was taken up by 

 Johannes Miiller about i84O. 4 That great observer demon- 

 strated the complete accuracy of Aristotle's description and the 



1 De generatione animalium, iii. 9 ; 758 a 37. 

 3 Historia animalium, i. 5 5 tfiop 1 35. 



3 Historia animaltum, vi. 10 ; 565^ 2. 



4 The history of this discovery is given by Charles Singer, Studies in the 

 History and Method of Science, vol. ii, Oxfoid, 1921, pp. 32 ff. 



