34 Hyhridization of Echinoids. 



Alteration in Physical Characteristics of the Cytoplasm of the 

 Egg by Action of Foreign Sperms. 



In my interpretation of the phenomena exhibited in the develop- 

 ment of Cidaris and its hybrids I have been influenced, to a consider- 

 able extent, by the consideration of facts concerning the transformation 

 of deutoplasmic materials to cytoplasm. The Cidaris egg, despite 

 its transparent character, contains a relatively large amount of yolk 

 and fat. This material gradually disappears as development con- 

 tinues. 



I have also been guided by results which I have obtained from 

 another inter-ordinal cross, Arbacia X Moira (Tennent, 1920). It 

 is unnecessary to review in this place the facts presented in that 

 paper, and it seems sufficient to say that certain granules and rods, 

 present in sections of cross-activated eggs and absent in sections of 

 straight-fertilized eggs, were explained as coarse precipitates formed 

 as a result of the emission of a foreign enzyme from the nucleus. 

 Even though we were to regard these bodies as artifacts produced by 

 the fixing fluid used (acetic-sublimate) — for we know that certain 

 metallic salts may cause the precipitation of proteids — the fact 

 remains that physical conditions in these eggs must have been differ- 

 ent than in the straight-fertihzed eggs which were fixed at corre- 

 sponding stages and in the same fixing fluid, and which show no bodies 

 of this kind. 



In continuation of the investigation mentioned above, one of my 

 students, Miss Hibbard, has made a study of Tripneustes eggs fertil- 

 ized with Lytechinus sperms, comparing these with the straight- 

 fertihzed and parthenogenetic eggs, and has found that in the cross- 

 activated eggs which are developing normally granules appear and 

 later disappear as the nucleus passes into the later phases of division. 

 Here, again, the only explanation seems to lie in the action of the 

 enzyme introduced by the foreign spermatozoon. Miss Hibbard 

 has also determined that some of the cross-activated eggs, which 

 segment less normally, show other and characteristic changes in their 

 cytoplasm. These changes are clearly pathological. 



The most striking result of the removal of cortical block followed 

 by cross-activation that has come within my experience is that 

 following the insemination of the Lytechinus egg, after preliminary 

 treatment with NaOH or CaCl, with the sperms of Holothuria 

 floridana (Tennent, 1911, p. 140). In this instance the sperm, upon 

 entering, in most cases tears the egg to pieces. A deep notch or 

 pathway made by the sperm may be seen and then the egg suddenly 

 disintegrates. In other cases the entrance of the spermatozoon is 

 followed by a slower, but none the less complete, cytolysis of the egg. 



Gray (1913) studied the eggs of Echinus acutus fertilized by the 

 sperm of Echinus escidentus and species-fertilized eggs of Echinus 



