6O I. F. McCLENDON. 



2. The Diclidestid. 



A. First Cleavage.- -The earliest stage I have of this is an 

 anaphase of the first cleavage (Fig. 25). It is similar to the 

 same stage in the preceding species save that the centrosomes if 

 they exist at all are larger and less dense, and the sphere reach- 

 ing the surface collects a considerable mass of cytoplasm around 

 it. The cleavage plane is " meridional " or more correctly, it is 

 perpendicular to the equator of the egg, but owing to the great 

 difference in size of the protoplasmic and yolk cells thus formed, 

 it does not pass through the animal or vegetal pole (Fig. 26). 



B. Second Cleavage. - - The yolk cell (cd~} is sometimes re- 

 tarded in division in Fig. 26 its nucleus is yet a mass of chro- 

 mosomal vesicles while that of the protoplasmic cell (cd~} has 

 reached a late prophase. Already a thickened layer of proto- 

 plasm marks the place where c 3 will be cut off. 



The protoplasmic cell (ah 2 } divides by a meridional (sagittal) 

 furrow into two cells, a s and 3 , almost equal in size (Fig. 27). 

 The yolk cell produces an elongated spindle similar to that in 

 the preceding species, one pole of which reaches the surface of 

 the egg to the right (left, when viewed from the vegetal pole) 

 of $ 3 (Fig. 27). The protoplasmic cell that is cut off (C 3 ) often 

 contains a considerable quantity of yolk (Fig. 28). Already a 

 thickened layer of protoplasm (Fig. 33) marks the place where 

 d^-' 1 will be cut off. 



In this and the two succeeding cleavages, the poles of the 

 yolk cell spindle are differentiated by the appearance of larger 

 granules on the astral rays of the posterior side of the sphere 

 that is to remain in the yolk (Fig. 27). This probably occurs 

 also in the first cleavage but I have not the right stage to show it. 

 These granules are probably homologous to lumps of cytoplasm 

 on the astral rays of Ltcmargns inuricatus. 



C. Third Cleavage. The division of the protoplasmic cells 

 <z 3 , ti\ and c 1 is equatorial (parallel with the face of the disc) 

 (Fig. 28). The yolk cell gives off a protoplasmic cell, d^~ to 

 the left of a*. Large granules appear on the astral rays of the 

 posterior side of the sphere left in the yolk. A thickened layer 

 of protoplasm marks the place where d : '-~ will be cut off. 



D. Foitrth Cleavage (Figs. 2930).- - In this cleavage the divi- 



