EMBRYOGENY 211 



sity or also the possibility of bringing forth the young 

 in water in any case ceased to exist. That in the first 

 place did not alter its embryogeny at all, and conse- 

 quently it still produces the larval form which now 

 appertains to its type. Experiments have also been 

 successful, which is not to be wondered at, in causing 

 it also to produce its young in the water, provided with 

 gills and a rudder tail. 



Such vacillations between inner and outer (free) 

 embryonic development are very often met with. 

 The c smooth shark of Aristoteles ' (Mustelus Icevis) 

 is viviparous in contradistinction to all other Sharks. 

 There are oviparous and viviparous insects and also 

 lizards. 1 



With regard to the viviparous Hill Lizard (Lacerta 

 vivipara) Kammerer states : c it is normally viviparous ; 

 the young, from three to ten in number, are, it is true, 

 often at the moment of birth still enclosed in the egg 

 skin, which, however, in a few minutes or hours they 

 burst open. If, however, the parent animals are 

 kept in an unaccustomed warm temperature of at 

 least 25C., then they lay eggs, whence the young cannot 

 so quickly escape ; at the first egg-laying period in 

 high temperature the time between laying and hatching 

 out is from three to nine days, the eggs are no more 

 numerous than before and have no shell; 3 . . . the 



1 The following details are taken from Vererbung Kiinstlichen Zeugungs- 

 und Farbenveranderungen of Dr. P. Kammerer in the Umschau, 1911, No. 7. 



2 In consequence of the heat the Lizards are also of a darker colour, 

 which is recognizable already in the embryo still inside the egg. 



P2 



