CHROMOSOMES IN THE SPERMATOGENESIS OF THE HEMIPTERA HETERORTERA. 137 



a longitudinally split, univalent element. Three other pairs of different sizes are 

 always to be seen {Di. 1, Dl. 2, l)i. 3) and sometimes a fourth {T)i. 4). The compo- 

 nents of each pair are equal in volume, but whether each pair is to be considered as 

 two diplosomes, or as the division products of a single one, I could not determine 

 since the number of chromosomes in the spermatogonia is unknown. 



Fird Maturation Division. — There are always 18 elements (Fig. 289), 17 large 

 and 1 (7^/. 1) much smaller. The latter is always bipartite (Fig. 29U), never quadri- 

 partite, and as will be evident from its later liistory is an univalent diplosome, and 

 from its .size perhaps correspondent to the two bodies marked Dl. 1 in the growth 

 period (Fig. 288). Of the 17 larger elements 1 must Ije the largest diplosome of the 

 preceding growth period {di. 1, Fig. 288), but at this stage it cannot ))e distinguished 

 with certainty from the other larger elements. In this mitosis the other small diplo- 

 somes of the growth period {Di. 2, Di. 3, Di. 4) are to be found neither in the spindle 

 nor in the cytoplasm. All 18 elements divide, and this is an equation division of the 

 large and small diplosome, but probably a reduction division of the 16 bivalent auto- 

 somes. 



Second Maturation Division. — There are 17 larger elements seen on pole views 

 (Fig. 291), 1 less than in the preceding spindle. This is because the large and small 

 diplosome have conjugated end to end, as one may ascertain by careful focussing {Di. 

 1, di. 1). Lateral views (Fig. 292) show that this bivalent element lies always slightly 

 out of the plane of the other chromosomes, and tliat each component of it is uncon- 

 stricted. Each of the 16 autosomes divides, but the components of the bivalent diplo- 

 some pass without division into opposite spermatids. Two daughter plates of the ana- 

 phase are reproduced, as drawn from the same cell at two levels ; one exhibits the 

 smaller diplosome {Di. 1, Fig. 293), while the other lacks this but shows the larger 

 diplosome {di. 1, Fig. 294). 



From the number of chromosomes in the maturation mitoses it may be concluded 

 that there are i^resent in the spermatogonia 32 autosomes and 2 diplosomes. 



Literature. — My previous account (1901i'>) confused the two maturation mitoses, 

 and did not describe the second one. 



40. Lygus pratensis Linn. 



Spermatogonic Division. — There were only 2 pole views, on the one I counted 

 33, on the other 34 elements. The correct number is probably 35 as we shall find. 



Groivih Period. — One large, longitudinally-split allosome can be distinguished 

 in the spermatocytes ; wliether there are others could not be determined. 



A. p. S— XXI. O. 24, 8, '00. 



