The Germ Cells of Diptera 367 



chromosomes and a smaller odd chromosome. This belief was 

 strengthened by the appearance of many metaphases and ana- 

 phases (Figs. 70, 71, 72) where the third portion of the figure (x) 

 seemed to be on the point of separating from the V-shaped element 

 next to it. This opinion was not confirmed however by the 

 composition of the spermatogonia! or oogonial equatorial plates, 

 nor was it possible to demonstrate with certainty a separate ele- 

 ment corresponding to x in the polar plates of the first spermato- 

 cyte mitosis or in the second spermatocyte. Fig. 72 is one of 

 several cases where the portion x seemed to be separated from 

 the two other elements of the group, but the separation must have 

 been only apparent, for one much oftener finds an anaphase Hke 

 Fig. J'7, where the separation of the heterochromosome group into 

 two unequal parts is certain (/zi, /z,). Sometimes the anaphase is 

 Hke Fig. 74, where more or less spherical masses replace the usual 

 V's of the heterochromosome group. Often all of the chromo- 

 somes except the smallest pair show in the metaphase that they 

 are elongated and V-shaped (Fig. 75), and in late anaphases 

 (Fig. 76) the elements of the two largest bivalents are usually 

 divided and the daughter chromosomes separated, often crossed. 

 Both here and in the second spermatocytes it is often difficult or 

 impossible to distinguish the heterochromosomes from the others. 

 In the telophase the chromatin forms a dense mass which loses 

 none of its staining quality and is soon resolved into the already 

 divided chromosomes of the second spermatocytes (Figs. JJ, 78, 

 79). A greater or less degree of elongation together with twisting 

 and fore-shortening makes it impossible to measure or even esti- 

 mate with any accuracy the relative length of the chromosomes, 

 so as to distinguish the two classes of second spermatocytes as 

 to size of heterochromosomes. Figs. 78 and 79 are two equa- 

 torial plates from the same cyst where the corresponding chromo- 

 somes are probably a — a, b — b, and h^ — /zj- All of the chromo- 

 somes divide in this mitosis. 



The oogonial metaphases are perfectly clear, and four equal 

 pairs of chromosomes are always present (Figs. 80, 81, 82). In 

 the metaphase they are usually grouped in pairs, and in the pro- 

 phase they are closely approximated and twisted. In fact this 



