96 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



Groom correctly described the radial arrangement of the protoplasm 

 as persisting for some time after cleavage. In my Figure 27 there is 

 represented a radial arrangement of granules which is a persistence of 

 the condition shown in Figure 2G as occurring at the close of the first 

 cleavage. The astrospheres have disappeared, and the nuclei lie near 

 the centres of the persisting radiations. This radial arrangement dis- 

 appears as soon as the second cleavage spindle forms (Fig. 28), but the 

 new radiations then formed may in turn persist after the cleavage until 

 the formation of the spindles for the third cleavage (Fig. 30). 



Groom ('94) states that two or more blastomeres may arise simul- 

 taneously from the yolk-cell ! " Similar cells [blastomeres from the 

 yolk-cell] are seen to arise in quite different positions at later stages, 

 .sometimes two or more at a time," (p. 138). Again, on page 140 he 

 writes : " In the early as in the later stages the merocyte before emerg- 

 ing from the yolk may not uncommonly be seen to give rise by division 

 to a second merocyte." Such conditions are represented in Groom's 

 Figures 17a (L. anatifera), and also in his Figures 53 and 57 (Balanus). 

 Certainly none of these figures really represents two blastomeres arising 

 at once. The two sets of radiations (asters) which Groom wrongly 

 interpreted as two " emerging merocytes" probably represent cases in 

 which the spindle was in such a position that both asters were visible 

 at the surface. Usually, however, only one aster is to be seen in the 

 living egg, the other being closely connected with the yolk. Sometimes 

 the spindle is long, so that the two asters are visible on opposite sides 

 of the egg. I have frequently seen the two sets of radiations in the 

 living egg, and sections show that the interpretation which I have just 

 given is the correct one. 



Sometimes multipolar spindles, which are probably the result of 

 abnormal conditions, are seen in sections of the yolk-cell, and these may 

 possibly result in a multiple cleavage. 



Rarely the cell c^ (Groom's "second blastomere ") may be formed 

 near the posterior end of the yolk-cell, as shown by Groom in his 

 Figure 13. 



Many other deviations from the regular course of cleavage have been 

 seen, but they are comparatively rare, and are to be regarded as abnor- 

 malities. Certainly they should not be interpreted as showing great 

 variability in the cleavage, as was done by Groom. I have noticed that 

 such cases are much more common when the animals have been kept 

 for some time in aquaria, but are rarely seen in eggs taken from ani- 

 mals whicli were recently removed from the open sea. 1 have attributed 



