No. 3-] THALASSEMA AND ZIRPHAEA. 591 



lines, giving rise at various nodal points to aster-like appear- 

 ances (PI. XXXI, Fig. 6). Where the strands converge to a 

 point between two microsomes, there is no focal granule, but 

 when they focus upon a granule (microsome) the latter is often 

 larger and more deeply stained than the surrounding micro- 

 somes, and a centrosome is thus simulated. This tendency to 

 form centers of radiation seemed especially marked in a slide 

 of eggs fixed by sublimate acetic (20^) while still within the 

 sexual pouches. It may be interesting to note that where the 

 eggs taken from the pouches have been allowed to remain in 

 sea water for some time without being fertilized, this appearance 

 becomes far less noticeable. Several preparations, one minute 

 after fertilization, show numerous minute centers of radiation 

 scattered irregularly throughout the cytoplasm, although more 

 abundant or more powerful about the animal pole. At least 

 ten were counted in a single section, some of which are closely 

 approximated, while others are some distance apart. The rays 

 are few (5 or 7), straight, and often short, though sometimes 

 equal to or longer than the egg radius. These can sometimes 

 be traced continuously without curving from one center to 

 another. At the center a granule is generally present, which 

 is distinguished from the neighboring microsomes by larger 

 size and a deeper staining power. Similar granules, however, 

 not the centers of radial systems, are to be met with through- 

 out the cytoplasm. These "asters" are to be distinguished 

 from the somewhat similar appearances in the unfertilized egg 

 by their greater distinctness and straighter rays. In prepara- 

 tions made two minutes after fertilization the radiations are 

 much more obscure, while in three-minute preparations and 

 later, they are scarcely, if at all, traceable, their place being now 

 taken by the definitive asters. 



It is evident that we have here a phenomenon at bottom 

 identical with that described by Mead ('97) in Chactoptenis. In 

 Thalassemia, however, the "secondary asters " are smaller and 

 less distinct, and do not push in the nuclear membrane as they 

 often do in Chaetopterus (cf. Mead). Moreover, I find no evi- 

 dence of a fusion of the " asters " or of any genetic relation 

 between them and the definitive polar asters, though it is not 



