BLATTELLA GERMANICA. II 



An attempt was made to determine the somatic number of chromo- 

 somes. The dividing cells of the follicles of young eggs seemed to 

 aflford the most favorable material, but even here there was so much 

 overlapping of the ends of the chromosomes that it was impossible to 

 be absolutely certain of the number. In the two most favorable cases 

 23 were counted (fig. 94). This differs from McClung's count for 

 similar cases among the Orthoptera, and Sutton's for Drachystoia 

 viagna. The eggs have so far resisted all efforts to learn what part 

 the odd chromosome may play in fertilization. 



Tenebrio molitor. 



In the metaphase of all spermatogonial mitoses where it was pos- 

 sible to count accurately, 20 chromosomes were found, 19 large ones 

 of approximately equal size, and i small spherical one (figs. 169, 170). 

 There is nothing in the resting nucleus of the spermatogonia which 

 would suggest either a nucleolus or an accessory chromosome. The 

 chromatin stains well during the whole growth period of the sperma- 

 tocytes, but it is impossible to separate the period into so definite 

 stages as in most other forms. 



In the youngest spermatocytes one finds occasionally a cyst con- 

 taining cells with nuclei like those of figures 171 and 172, indicating 

 that a brief ' ' synapsis ' ' or condensation stage occurs at the close of 

 the last spermatogonial mitosis. During the greater part of the period 

 the chromatin forms a heavy, irregular, and often segmented spireme 

 (figs. 173, 174). Shortly before the first maturation division, such 

 split segments as appear in figure 175 are sometimes found ; some of 

 these simulate tetrads with slender connecting bands between the 

 paired elements. Again, one finds a few cases like figure 176, where 

 the spireme is segmented into bivalent chromosomes, each component 

 showing a longitudinal split. This figure also shows the small chro- 

 mosome. Usually, however, the irregular and much tangled spireme 

 (figs. 173, 174) condenses into a heavy segmented band variously dis- 

 posed in the nucleus (fig. 177). This band soon separates into the 

 bivalent chromosomes shown in figures 178 and 179, giving 9 sym- 

 metrical pairs and i unsymmetrical one (fig. 179 s) composed of the 

 small chromosome and a much larger mate. In the prophase of the 

 spindle, in rare cases, some of the chromosomes are longitudinally 

 split and transversely constricted, forming tetrads (fig. 180), but more 

 often they appear as in figure 181. The unequal pair appears in each 

 figure at s. In the metaphase (fig. 182) it is the last to come into the 

 equatorial plate, possibly because of its lack of symmetry. The smaller 

 component of this pair is always directed toward the equator of the 



