No. 3.] THALASSEMA AND ZIRPHAEA. 603 



III. The Chromatin. 

 a. In Maturation. 



Among the early egg-clusters are some in which the chro- 

 matin of every cell is arranged in a thick, rough, dark-staining 

 spireme, in which occasional indications were observed of the 

 longitudinal splitting so frequently observed in other forms at 

 this period. It is impossible to say with certainty whether this 

 spireme consists of a single thread or several — a difficulty 

 that has frequently confronted other observers. It is coiled in 

 several turns about the nuclear membrane, against the inner 

 wall of which it seems to be principally situated (PI. XXXI, 

 Figs. I, 2). Lack of earlier stages has prevented the work- 

 ing out of the genesis of this spireme. In later egg-clusters 

 are cells containing a spireme in all respects similar to the 

 above-described, except the commencing transverse division 

 and marked indications of the longitudinal fission (PI. XXXI, 

 Figs. I, 2). In other cells of the same cluster this process 

 has advanced one step further, the spireme being now com- 

 pletely divided into segments connected by numerous linin 

 strands (PI. XXXI, Figs. 3-5) and partially cleft longitudi- 

 nally to form stout and much-flattened rings. The transverse 

 division appears to be followed by a shortening and concentration 

 of the resulting segments, obliterating their granular appear- 

 ance (see Hacker, '95, Canthocamptus, for similar phenomenon). 

 Although the exact number of these segments is not easy to 

 determine, they are readily seen to be nearer twelve than 

 twenty-four, which clearly indicates that the chromosomes first 

 appear in the reduced number as in so many other forms. 



Meanwhile a fine nuclear reticulum is gradually developed, 

 which readily takes the plasma stains, and could not be made 

 to take the pure chromatin stains. Throughout the entire 

 growth period it increases in bulk and distinctness until, in the 

 full-grown ovum, it fills the entire germinal vesicle (PL XXXI, 

 Figs. 3-6). During prophase of the first maturation divi- 

 sion, after exhibiting a marked increase in its affinity for iron 

 haematoxylin, it is rejected bodily by the spindle and degen- 



