On tlie Dimegalous Sperm and Chromosomal Variation of Euschistus, etc. 123 
follicle 2). Conseqiiently the speriiiatids of follicles 1 (fig. 6) and 3 are 
constantly lai'ger than spermatids of the other follicles (fig. 13, follicle 2). 
The same relations can be seeii in any one of the testes, and the case of 
figs. 57 and 58, PI. X, exliibits the average comparative sizes of fü'st 
sperniatocytes froni another testis. These relations are as described in 
niy earlier paper, though then they Avere not followed beyond the stage 
of the early sperinatid. 
The compaiison of the sizes of the full formed spermatozoa had to 
be inade upon the study of rather thick sections, for smear preparations 
were impracticable since in them spermatozoa froni different follicles 
would become mixed together. In such sections the whole head of the 
sperm can be found intact whenever the sperm bundles he directly in the 
plane of the section, but the flagella ai'e so niuch longer than the head, 
and often so sinuous, that they can never be followed A\ith certainty in 
theh- full length. Thus only sperm heads could be compared and not the 
flagella. Only such spermatozoa were studied as lay at the distal ends 
of the follicles, all such sperm being fuUy formed. The results may 
be seen at a glance at PI. IX: the sperm heads froni follicles 1 (fig. 7) 
and 3 (figs. 24 — 26) are in aU cases markedly longer than those froni fol- 
licle 2 (figs. 14, 15), 4 (figs. 28, 29), 5 (figs. 31, 32) and 6 (figs. 35, 36). 
There is some individual Variation in the length of the sperm heads of a 
]iarticular follicle, as illustrated in the two extreme sizes froni follicle 2 
(figs. 14, 15), the three froni follicle 3 (figs. 24 — 26), and the extremes 
of size found in follicles 4 (figs. 28, 29), 5 (figs. 31, 32) and 6 (figs. 35, 36). 
AVhether the size differences of sperm froni the same follicle are true in- 
dividual differences, or only differences in state of loconiotion (contrac- 
tioii), was not deterniined. But hoivever this may be, the sperm heads 
of foUicles 1 and 3 are invariably niuch larger than the kargest froni the 
other follicles . It is probable that there are even greater differences in 
the flagella, though this could not be deterniined. Sperm heads froni 
the vas deferens also exhibit size differences like those found in the folh- 
cles of the testis. 
The differences of the sperm heads seem to be one nierely of size, 
especially length. The terminal acrosonie (a of the figimes) is iisually a 
narrow tlu'ead, though sometimes branched, in the case of sperm of the 
first (fig. 7) and thh'd (figs. 24 — 26) follicles, Avliile it is more usually bifid 
in the case of the sperm of the other follicles (figs. 14, 15, 28, 29, 31, 32, 35, 
36). This difference may, however, not be constant but be due to pseudo- 
podial extension of this part, for it is this portion that conies in dosest 
contact Anth the nurse cells. 
