SPERMATOGENESIS OF EUSCHISTUS _ 789 
little influenced by the centrioles. In Euschistus they lie quite 
irregularly in the spermatocytes, and generally each thread fails 
to divide in one of the maturation mitoses; further, it is a matter 
of chance at what point a mitochondrial thread becomes divided. 
They become irregularly divided in the two maturation divi- 
sions so that varying amounts of them become apportioned to 
the spermatids.22 That there is no accurate quartering of the 
mitochondria in a number of other species results from a study 
of the figures of various writers, such as the Schreiners (’05, 
Myxine), Meves (’00, Paludina, Pygaera), Gross (’06, Pyrrho- 
coris), Wassilieff (’07, Blatta). But in the bee and hornet 
(Meves, ’07, ’08), in Pamphagus (Giglio-Tos, ’08), in Blaps 
(Benda, ’03) and Stenobothrus (Gérard, ’09) they appear 
more evenly arranged around the spindles, and in these objects 
probably become more regularly divided. But there is good 
evidence that in certain cases it is a matter of chance how they 
become divided, in which regard they differ markedly from the 
chromosomes. 
The mitochondria in the spermatid of Euschistus coalesce 
to produce the true Nebenkern, which elongates and forms a pair 
of narrow bands lying on the sides of the axial thread and 
extending from the head probably to the end of the tail of the 
spermatozoon. A similar metamorphosis of the Nebenkern is 
known for flagellate spermatozoa in a number of invertebrates, 
while in the mammals the mitochondria engender a spiral fila- 
ment around the middle piece. There is now, however, consider- 
able evidence that in many forms of flagellate spermatozoa, 
such as those of mammals and molluscs, the whole tail enters 
the egg in fertilization, and is not left outside the egg (contrary 
to earlier observations); therefore it is probable all the mito- 
chondrial substance of the sperm enters the egg; much more 
substance, accordingly, than merely the chromatin of the head. 
Since then fertilization brings together the mitochondria 
of two parents, it now becomes of great importance to trace 
22 T have previously intimated, (’10b) the possibility that the relative amount 
of the mitochondrial substance received might determine the sex-preponderance 
character of a sperm, a matter unfortunately very difficult to test. 
