188 H. M. WOODCOCK. 



(b) Ookinete of Male Character and its s u b s e t{ u e n t 

 development in the Gnat. 



Ookinetes which will produce male forms are easily dis- 

 tinguishable from those of indifferent character. The cyto- 

 plasm (fig. 9) is almost hyaline^ and much clearer than in 

 the indifferent ookinetes, which occupy, in this respect, a 

 position intermediate between the other two forms. Reserve 

 materials are completely lacking. The body is smaller than 

 that of either of the other kinds of ookinete; the nuclear 

 apparatus is, however, much larger relatively to the cytoplasm, 

 and very rich in chromatin. The earliest nuclear changes 

 which take place are, apparently, similar to those above 

 described, and lead to the union of the chromatin of the two 

 nuclear constituents. A heteropolar spindle is next formed, 

 and the chromatic elements divide, half being drawn to 

 either end. 



It is clear from the subsequent development, however, 

 that this division is in a different sense from the corre- 

 sponding one in the indifferent ookinetes. Instead of the 

 trophic constituents being separated from the kinetic ones, 

 we must consider the male elements of both kinds as being 

 grouped together and separated from the female ones. The 

 smaller, more condensed half (9 b) is entirely male in cha- 

 racter, while the larger, looser half is of female sex. This 

 latter nuclear body, Avliich remains contrail}^ situated (c and 

 D,f.n.), is not to be regarded, therefore, merely as a tro- 

 phonucleus, but as containing the female elements belonging 

 to both tropho- and kineto-nucleus. It rounds itself off, but 

 takes no further part in development, gradually disappearing 

 in situ and being finally left behind with the unused cyto- 

 plasm (fig. 9 p). The male nucleus, on the other hand, 

 divides successively to form eight nuclei (c and d, m.n.), 

 which become uniformly distributed throughout the body of 

 the microgametocyte, as the male ookinete may now be 

 termed. Each of these nuclei is, moreover, double, the 



