122 chromosomes in the spermatogenesis ov the iiemii'tera iietekoptera. 



LYGJEIDjE. 

 25. CEdancala dorsalis Sa}'. 



Spermatof/onic Diruion. — The spindle contains 13 elements (Plate XII, Fig. 1S3). 

 These are: 2 diplosomes of approximately equal volume, the smallest of all {Di, 

 di) ; 1 monosome (Mo), the only unpaired element ; and 5 pairs of autosomes {A, a-E, 

 e) of which the pairs are to be recognized rather l)y peculiarities in form than in size. 



Growth Peril))]. — Up to the late postsynapsis the allosomes cannot be distinguished 

 from the autosomes, that is. they neither remain dense and compact nor do they con- 

 tinue safraninophilous. It is, accordingly, probable that until then the allosomes 

 undergo changes parallel to those of the autosomes, except, as will appear from the 

 later history, the monosome remains a single element and the diplosomes probably do 

 not conjugate, while the 10 autosomes go to compose 5 longitudinally split bivalent 

 chromosomes. Throughout there is a large plasmosome {PI, Figs. 184, 185), lying 

 usually against the nuclear membrane. The growth period is closed by an almost com- 

 plete rest stage (Fig. 185), one in which the chromosomal boundaries cannot be well dis- 

 tinguished. Just before this rest stage there becomes visible a safraninophilous double 

 body [Mo, Fig. 184) placed almost invariably upon the plasmosome ; we shall find 

 that this is the monosome. It reappears first in the form of a pair of rods, each finely 

 granular, which are to be considered the split halves of the monosome because they 

 are of equal length and volume ; at this stage the two are more or less curved so that 

 together they bound an oval space. They soon become compacter w^ith smooth sur- 

 faces, and appear as two shorter parallel rods (il/o. Fig. 185). No trace of the diplo- 

 somes is to be seen, i. c, they do not stain difterently- from the autosomes. 



First Maturation Division. — In the earl}^ prophases the plasmosome dissolves 

 without a visible remnant. The monosome (il/o. Figs. 186, 187) has the form of two 

 short, thick rods, which may be parallel but are more frequently divergent. The 

 autosomes now commence to stain with safFranine (Figs. 18C, 187), and they compose 

 5 bivalent elements in which each univalent component is longitudinally split; this 

 split gradually narrows up to the stage of the metaphase. And now reappear for the 

 first time the diplosomes {Di, di, Figs. 186, 187) as two very small elements, each in 

 structure and stain like a miniature univalent autosome ; they are not in contact with 

 each other in any part of the prophase, but are more or less widely separated ; some- 

 times each appears longitudinally split (Fig. 187). By their size relations there can 

 be no doubt which of these various nuclear structures are tlie diplosomes and which 

 is the monosome. In tlio late prophases (Fig. 188) the monosome (Mo) changes 

 form so that eacli of its halves becomes spherical; the diplosomes {Di, di) become 



