EMBRYOLOGY OF CLEPSINE. 23'3 



water, begins to diminish, and soon the yolk and membrane 

 are in contact, the polar g^lobule being pushed so far back into 

 the yolk that it is seen with dithculty. The membrane now is almost 

 in contact with the yolk all around, and the egg has again the form 

 of fig. 1. After fifteen minutes the yolk begins to recede again 

 from the membrane, initiatory to the expulsion of the second polar 

 globule. The exit of this globule is not attended with so marked 

 and regular constriction as the first. The expulsion of the two 

 globules is completed in 45 — 55 min. (1 h. 15 min.). 



In C. complanata this prociss is accomplished in the same 

 manner as already described for C. margiuata. The constriction 

 often appears (0. complanata) raised in the middle, giving it the 

 appearance of beiiig double. In tlie egg of C. heteroclita the 

 constriction is less conspicuous, but is, nevertheless, unmistake- 

 able. I have not been able to see the stages preceding the 

 cleavage in C. bioculata. 



The process just described cannot be compared with the irre- 

 gular movemi ments of an Amoeba. They begin at a definite 

 time, proceed in the same regular manner, and are accomplished 

 in about the same time on each egg. Thus far no such constric- 

 tion has been observed on the egg of any other animal. The 

 "slow periodical changes in form" observed by Flemming (yVVj 

 Anodonta), " the attempts to divide " reported by Brandt ( ^--Vj 

 Ascaris), the " form-changes " noted by Schultz (-,1-^, Torpedo), 

 the "contractions" and so-called "amoeba-like movements^' 

 described, from time to time by other authors, as preceding or 

 accompanying the expulsion of the polar globules, may be more 

 or less modified forms of the same phenomenon. 



No polar globules were recognized by Grube, nor by Leuckart 

 and Rathke. It is evident, however, that the polar globules were 

 seen by all these investigators ; for they saw one or more small 

 " balls '' between the first two cleavage-spheres, i.e., before the 

 production of ectoblasts. Biitschli (V)» ^'i ^^i^ excellent work 

 on "Cell-division and Conjugation of the Infusoria," has inter- 

 preted Grube's polar ring as a polar globule ; but this is cer- 

 tainly incorrect, as an examination of the ring will show. That 

 the polar globules are produced by the archiamphiaster,^ and 

 that they are not therefore mere " buds " of yolk, having no 

 genetic connection with the germinal vesicle, as supposed by 

 Bobin ('^^), is proved by such sections as that given in tig. 

 63, Plate XIII. This section shows the second polar globule in 



' Fol (%*, ff ), who has followed this process in the living egg (Asterias), 

 thinks that the Archianiphiaster does not produce dh-ectly the iiolargiohule, 

 but that it gives rise to a second amphiaster, and that the latter produces 

 the first polar globule. 



