272 



MEAD. 



[Vol. XIII. 



can be predicted at least as soon as the first maturation spindle 

 appears, and before the sperm enters the egg. 



It is clear that the determining factor is neither the path of 

 the spermatozoon, for the relation of the latter to the direction 

 of the spindle varies ; nor the path of the female pronucleus in 

 approaching the male pronucleus, for the two male centers 

 have already assumed their permanent position. 



The first furrow is meridional as usual, and sinks in all 

 around the egg at the same time, as in Lepidonohis. During the 

 first cleavage a peculiar lobe is normally formed on the lower 

 hemisphere, first becoming noticeable when the spindle is in 

 the equatorial-plate stage. It is composed very largely of yolk, 

 although protoplasmic rays from the astrospheres run through 

 it to the periphery. Every phase in the development of this 

 lobe bears a constant relation to that of the karyokinetic 

 spindle (Fig. 117, 118, etc.). During the later phases of the 

 karyokinesis, — the reconstitution of the nuclei, — the lobe be- 

 comes constricted at its base, and finally, by the time the new 

 nuclei have assumed a spherical form, is completely resorbed.* 



The cell CD, which bears the lobe, 

 is larger than AB. In these two cells 

 the whole karyokinetic process from 

 first to last is carried on simultane- 

 ously. The spindles in the two cells 

 are inclined to each other, as in 

 Amphitrite (left-oblique cleavage). 



The four resulting cells divide 

 simultaneously into eight, in the 

 usual direction. Of the 8-cell stage, 

 the four vegetative cells are, as usual, 

 larger than the four animal cells, and one cell, DD^, is largest 

 of all (text Fig. XXI). The 8-cell stage of this form is 

 peculiar, however, in that one of the four apical cells, d, is 

 much larger than the other three. There are in this stage two 



Fig. yiyA. — ChcEiopierus, 8-cell 

 stage from lower pole. 



* I said in my previous paper that the lobe was completely constricted off. 

 The statement was based on the study of preserved material which certainly sup- 

 ported this interpretation ; but an examination of living eggs plainly shows that 

 I was in error 



