MUSEUM OF COMPARATIVE ZOOLOGY. 491 



osmic acid shows that the vesicle is the " cone d'exsudation " swollen 

 by the action of the acetic acid. 



In the case of abnormal fecundation, where two or three of the male 

 asters have united with the female nucleus, the remaining male asters 

 are very regularly placed at equal distances from each other and at 

 about a third of the distance from the surface to the centre of the yolk. 

 This proves (1.) the attraction of the male asters for the female nucleus 

 up to the time of its saturation, and (2.) the mutual repulsion of the 

 male asters, for otherwise their arrangement, irregular at their first 

 appearance, would not subsequently become regular. Eggs that have 

 received two spermatozoa have always been seen to form a tetr aster 

 instead of an amphiaster at the first segmentation. In certain cases of 

 sea-urchins kept a short time in confinement, a large majority of the 

 artificially fertilized eggs have exhibited the tetraster ; almost all the 

 larvae were monsters. It is possible in certain vegetables, and even in 

 certain animals, that the tetraster may not be a pathological phenome- 

 non, but in the sea-urchin and starfish it is positively pathological as a 

 rule, and it is doubtful if such an Qgg can produce a normal larva. 



FoL ('77^) has also published a reply to the criticisms of Perez and 

 Giard, which is more extended than any of the papers cited ; but since 

 it contains nothing essentially new, a review of it will be unnecessary, 



Hatschek (77^ pp. 503-505, Taf XXVIII. Fig. 1) finds within the 

 pear-shaped egg membrane of Pedicellina (whether vitelline or second- 

 ary membrane is left unsettled) sometimes a small, sometimes a large 

 number (50) of active spermatozoa. This is evidence of the existence of 

 a micropyle. At the vegetative pole of an egg which had two polar 

 globules there was seen a clear protoplasmic bod}'', free from yolk gran- 

 ules, which, in the course of two or three minutes, became lost to vision 

 by sinking into the yolk. Hatschek considers this a metamorphosed 

 spermatozoon ; but it seems probable that it should rather be compared 

 with similar hitherto unexplained protoplasmic protuberances from the 

 vegetative pole of the egg which usually occur after impregnation.* 



A possible objection to this view exists in the fact that these pro- 

 tuberances are not always destitute of yolk granules, as Hatschek affirms 

 of the body he has observed ; but this may be subject to variation in 

 different cases. 



Hoffmann ('77, p. 19) has observed in the case of Malacobdella that 

 the spermatozoa do not always penetrate the yolk with the head end, 

 but often bore in with the tail end, and continue in activity for an hour 



* Compare Whitman '78« pp. 21, 39, and 0. Hertwig '78« Taf. XI. Fig. 4. 



