118 CHROMOSOMES IN THE SPERMATOGENESIS OF THE HEMII'TERA HETEROPTERA. 



of cases two of the larger autosomes were found closely applied side to side and in the 

 preceding late prophases this is also sometimes the case. 



Second Maturation Division. — Again 7 elements are found (Fig. 141), the smalle.st 

 of which is the diplosome, the nonconstricted one the monosome {Mo). All of these 

 divide except tlie monosome which passes wholly over into one of the spermatids, as 

 shown clearly in the anapliase illustrated in Fig. 142 where one daughter plate shows 

 7 and the other only 6 elements. The monosome frequently lags behind the others 

 in reaching the spindle pole (Fig. 143). 



Literature. — My preceding account (1001//) was very brief, I overlooked the mon- 

 osome entirely and erroneously gave 14 chromosomes as the normal numl)er. Wil- 

 son (1905c, 1906) has correctly emended my observations and has given a good series 

 of figures, but he failed to note that the dij^losomes are unequal in size. 



20. Alydxis eurinus Say. 

 My earlier accounts (19016, 1905 p. 194) were correct, except that I failed to note 

 that the allosome of the growth period {Mo, Plate XI, Fig. 145) is the odd chromo- 

 some, i. e., the monosome, and not a bivalent diplosome; there is no trace during the 

 growth i)eriod of the very minute diplosomes. The monosome is rather ovoid in the 

 synapsis period, but it later becomes more elongate and longitudinally split (this split 

 shows usually simply as an indentation at either end, but sometimes as a fine clear 

 line along the whole length). Its division in the first maturation mitosis (Fig. 147) 

 is in the line of this split, therefore equational. A daughter chromosomal plate of 

 this division is reproduced in Fig. 148 ; the monosome is the only element that 

 appears unconstricted, while all the others, including the small central diplosome {Di), 

 show a constriction that is the longitudinal split reopening for tlie next mitosis. In 

 the second mitosis there are again 7 elements, all of which divide except the mono- 

 some {Mo) that passes without division into one of the spermatids. In the spermato- 

 gonium (Fig. 144) the 13 chromosomes make up 5 pairs of autosomes (.1, a-FJ, e) one 

 pail- of diplosomes {Di, di), and the monosome {Mo). The whole spermatogenesis is 

 quite similar to that of the preceding form. 



21. An ASA tristis De Geer. 



Spermatogonic Divisions. — In seven very clear pole views 21 chromosomes could 

 be counted. These are (Plate XI, Fig. 151) : 2 small rounded bodies, not quite equal 

 in size, the diplosomes {Di, di) ; a longest unpaired one that is sometimes constricted, 

 the monoisome {M<i) ; and a series of 9 pairs of autosomes {A, a-I, i). 



(irouih Period. — The large allosome of the growth period is the monosome {Mo, 

 Figs. 152-155), which remains compact and safraninophilous. It is irregularly elon- 



