CHROMOSOMES IN THE SPERMATOGENESIS OF THE HEMIl'TERA HETEROrTERA. 121 



24. Metapodius terminalis Dall. 



Spermafogunic Divinons. — Two pole views of the chromosomes are shown in 

 Plate XI, Figs. 169, 170. Each shows 2 very minute elements which are unequal in 

 size and ai'e the diplosomes [Di, di). Then there is one unpaired, constricted element, 

 the monosome [Mo). The remainder are 9 pairs of autosomes {A, a-I, /). 



Growth Period. — Throughout this period there is a dense safraninophilous body 

 of considerable size close to the nuclear membrane {Mo, Plate XII, Figs. 171-173) ; it 

 is ovoid in the synapsis, more elongate in the postsynajisis, ovoid again in the (incom- 

 plete) rest stage ; it never appeal's double as if formed by the conjugation of two 

 elements, nor any at any period shows clearly a longitudinal split. This is probably 

 the monosome because it is far too large to be the bivalent diplosome. No sign at all 

 of the diplosomes is to be seen ; this may be either on account of their very small size, 

 or perhaps on account of their not retaining a compact form. The 18 autosomes con- 

 jugate end to end to form 9 bivalent ones. 



First Maturation Division. — In the prophases (Fig. 1 74) reappear the diplosomes 

 {Di, di) as a pair of small rounded bodies, not attached together until the time of dis- 

 appearance of the nuclear membrane. In the spindle the 11 elements show a very 

 regular disposition (Figs. 170, 177) like that of Ana. m tristis, with the bivalent diplo- 

 some in the center and the monosome {Mo) excentric. All these elements are shown 

 on side view in Fig. 175 : there the diplosome is seen to have its components of dis- 

 similar volume, and to divide reductionally as do the 9 bivalent autosomes. But the 

 monosome {3Io, Fig. 175), when examined in profile, is seen to be jilaced with its 

 long axis in the plane of the equator and to divide thi'ough its length. As the 

 daughter chromosomes separate in the anaphase (Fig. 178) a constriction upon each 

 marks the reopening of the longitudinal split ; but the monosome (Mo) does not 

 show this constriction, and upon pole views of a daughter plate (Fig. 179) appears 

 simply ovoid while all the others are dumbbell-shaped. 



Second Maturation Division. — In the spindle the chromosomes are again differently 

 arranged (Fig. 180), they are 11 in number; the diplosome (tW) can be recognized by 

 its small size, the monosome {Mo) by its small depth. All of these divide again except 

 the monosome which passes without division into one of the spermatids {Mo, Figs. 

 181, 182). 



Literature. — In my previous brief account (1901&) I did not describe the second 

 maturation division, gave the number of spermatogonic chromosomes as 22 (counting 

 the constricted monosome as 2), and in the growth period confused the monosome 

 with the diplosomes. '■ 



a. p. S.— XXI. M. 23, 7, 'Ofi. 



