Ill DIFFERENTIATION 103 



abundant at the higher temperature. This is an inheritance 

 from the female parent (Sphaer echinus), in the pure type of 

 which a rise of temperature has the same effect. Of the 

 number of roots in the anal arms it is impossible to make 

 a definite statement since heat increases these in both parents. 

 The ratio of the length of the apical to the length of the 

 anal arm is 1 in Strongylocentrotus, and greater than 1 at 

 the higher temperature, O5 in Sphaerechinus and decreased 

 at the higher temperature, while in the hybrids it approaches 

 0*5 at higher, 1 at lower temperatures ; this appears therefore 

 to be determined from the female side. 



Other means have been used by Herbst to displace the 

 inheritance to the female side, namely, the combination of 

 artificial parthenogenesis with cross-fertilization. The egg is 

 thus given an initial impetus towards the development of the 

 maternal characters : the paternal are then superadded. 



To this end the ova (of Sphaerechinus) are treated with 

 butyric or other fatty acid, and subsequently with sea-water, 

 in such a way that while the fertilization membrane is not 

 thrown off, the nucleus yet enlarges and becomes indistinct, 

 suggesting the passage of substances from it into the cyto- 

 plasm. After a suitable interval they are fertilized (by 

 Strongylocentrotus sperm). Irregular segmentation follows 

 and larvae are produced which have a greater similarity to 

 larvae of the pure Sphaerechinus type than have the ordinary 

 hybrids, though they are not completely of that type. The 

 increase of maternal characters is evinced by the greater 

 number of cross-bars in the anal arms, the greater number of 

 roots to the anal arms, the greater length of the oro-apical 

 branch, the branched extremity of the apical arm and by 

 the decrease in the ratio of apical to anal arm (less than 0-5). 



Cytological examination shows that the sperm always 

 enters, rotates, and develops its sphere and centrosome. The 

 female nucleus is in some cases only just resolving itself into 

 chromosomes, in others this has occurred and the monaster 

 has appeared. 



In the first case the male and female nuclei unite and 

 a fertilization spindle appears. On it are thrown both sets of 



