50 Chemical Basis of Genus and Species 



related sea urchin, S. JranciscanuSy the hereditary 

 effect of the spermatozoon is seen very distinctly in the 

 primitive skeleton formed by the larva.' (Fig. 3.) 

 In the case of the heterogeneous hybridization the 

 spermatozoon acts practically only as an activating 

 agency upon the egg and not as a transmitter of paternal 

 qualities. 



The second striking fact is that while the sea-urchin 



Fig. 3. Five-days-old larvae of two closely related forms of sea 

 tirchins (S. purpura tus 9 and S. franciscanus cf). In this 

 case the larva has also paternal characters as shown by the 

 skeleton. 



eggs fertilized with starfish sperm develop at first 

 perfectly normally they begin to die in large numbers 

 on the second and third day of their development, and 

 only a very small number live long enough to form a 

 skeleton; and these are usually sickly and form the 

 skeleton considerably later than the pure breed. It is 

 not quite certain whether the sickliness of these hetero- 

 geneous hybrids begins or assumes a severe character 



' Loeb, J., King, W. O. R., and Moore, A. R., Arch. /. Entwicklngs- 

 mech., 1910^ xxix., 354. 



