Early Influence of Spermatozoan Characters of Echinoid LarvcB. 135 



THE CIDARIS FEMALE BY TOXOPNEUSTES MALE CROSS. 



The cross is easily made, the Cidaris eggs requiring no treatment in order 

 that fertilization may be accomplished. The eggs may be fertilized with Tox- 

 opneustes sperm immediately after their removal from the ovary, but 

 as a check against the possibility of chance 

 fertilization with Cidaris sperm they were kept 

 for 2 hours before inseminating with the foreign 

 sperm. More than 90 per cent of the eggs fer- 

 tilized; the typical fertilization membrane ap- 

 peared shortly after the addition of the sperm. 

 In this cross no difference from the characteristic 



normal Cidaris development was noted before ^^^ g. -Optical section of portion 

 the beginning gastrula stage. The fertilization- o;^j^-CS%rfm^y''m^^^^^^^^ 

 cleavage interval was not lessened, as in the case teiisatbaseof archenteron. 24 hours, 

 of certain other echinoid crosses that I have de- 

 scribed. In point of time the appearance of the mesenchyme seemed 

 slightly hastened, although the gain in time is not great enough to war- 

 rant a general conclusion, since it is quite within the range of variation 

 between different lots of straight-fertilized eggs. My statement regard- 

 ing a possible slight hastening refers to comparative straight and cross 

 fertilization in the same lot of eggs. Even here I prefer to draw no con- 

 clusions, since I have made the comparison with only eight lots of eggs. 

 As to the place of mesenchyme formation there is no chance for either 

 personal equation in the observer or individual variation in the larvae to 

 play a part. 



Figs. 9 and 10.— Optical section of ToxopneusUs cf X Cidaris 9 gastrula, 

 showing primary mesenchyme cells. 24 hours. 



In the hybrids the mesenchyme arises from the sides and around the 

 base of the archenteron, close to its point of union with the blastopore 

 (figs. 8, 9, 10). This was true in every instance. The difference between 



