364 N. M. Stevens 



5 Phorbia bras sic a 



Only one male of Phorbia was obtained and only four stages 

 drawn; but these indicate precisely the same conditions as in the 

 other species examined. Phorbia belongs to the sub-family 

 Anthomyiinae. Fig. 37, a growth stage; 38, a prophase; 39, a 

 metaphase; and 40, an anaphase, show clearly the presence of an 

 unequal pair of heterochromosomes resembling those of Musca 

 domestica. 



6 Scatophaga pallida 

 y Tetanocera sparsa 



The chromosomes of Scatophaga and Tetanocera resemble each 

 other so closely in number, form and behavior that they will be 

 considered together. Fig. 41 is a spermatogonia! prophase of 

 Scatophaga; and Figs. 42 and 43, spermatogonia! prophase and 

 metaphase of Tetanocera. All show equally paired ordinary or 

 V-shaped chromosomes and unequally paired heterochromosomes. 

 Figs. 44 and 45 are prophase and metaphase of the first spermato- 

 cyte of Scatophaga, Figs. 46 and 47 the corresponding stages for 

 Tetanocera. In both species it will be seen that there is a close 

 resemblance between the paired condition of the chromosomes in 

 the prophases of a spermatogonia! division and of a first spermato- 

 cyte mitosis. In general the chromosomes were larger in the 

 spermatogonia (Figs. 41, 42, 43) than in the spermatocytes (Figs. 

 44j 45' 46? 47)> but frequently prophases of spermatocyte mitoses 

 could be certainly identified as such only by the metaphases in 

 the same cyst and the growth stages in the neighboring cysts. 

 The only actual observable diff"erence between the synaptic con- 

 dition in the spermatocytes and the spermatogonia is the behavior 

 of the pairs in the following mitosis: in the spermatogonia the 

 members of the pairs separate in metaphase (Fig. 43), and each 

 divides in metakinesis; while in the spermatocytes the members of 

 each pair remain closely associated in metaphase (Figs. 45 and 47) 

 and separate in metakineses (Fig. 48), but do not divide until the 



