ZOOLOGY AND BOTANY, MICltOSCOPY, ETC. 
101 
one Siphonophore (and four more superficially), one Pteropod, one 
(Jephalopod, one Polyclnete ( Eteone pterophora ), and Salpa virgula 
among Tuuicates. The terminology adopted is that of La Yalette St. 
George. 
The general conclusions to which his investigations have led the 
author are summarily stated. He regards spermatogenesis proper as 
nothing hut the change in form of a cell in a definite way ; its object is 
to fecundate the female cell, and the development of the spermatozoon 
from the spermatid is only a secondary phenomenon of adaptation which 
serves to facilitate the meeting of the two cells. The present studies 
serve to confirm the doctrine that the nucleus of the spermatid forms 
the head or body of the spermatozoon, and the author believes that 
in time all animal spermatozoa will be found to have a more or less 
normally constituted nucleus. This nucleus, however, is not a homo- 
geneous whole or formed of a single substance ; we may distinguish 
in it the nuclein or chromatin and the nuclear plasma or karyo- 
plasma. The relations of these two vary very considerably with the 
stage of the development of spermatozoa ; where kinetic division is 
going on the nuclein and the karyoplasma are sharply differentiated. 
Most fixing reagents give a sort of structure to the nuclei, but Dr. 
Pictet thinks that this structure is only an artificial modification of 
the nuclear substance. If, as he thinks, the nucleus is dissolved in 
the karyoplasma, the addition of an acid, which does not dissolve the 
nuclein, will cause it to be precipitated in a more or less granular 
form. It is only after the penetration of the spermatozoon into the 
ovum that the nucleus takes on a structural form to fuse with the 
female nucleus. The author believes that the karyokinetic division 
of the spermatocytes has the object of furnishing each seminal cell 
with a nuclear substance, which has exactly the organic and chemical 
constitution necessary for fecundation. When, towards the end of 
spermatogenesis, direct division occurs, its object is that of giving to 
each spermatid the amount of nuclear substance necessary to the for- 
mation of a spermatozoon. 
The necessary locomotor organ is provided by the cytoplasm of 
the seminal cell, which forms what is ordinarily known as tbe tail 
of the spermatozoon. The volume of this tail is generally much 
smaller than that of the cytoplasmic part of the tail that has been 
used up in forming it ; there is clearly a condensation of the proto- 
plasm with the object of giving more rigidity to the caudal filament, 
and allowing it to resist the movement, often of some violence, by 
which it is affected. 
The cellular membrane may be generally seen easily in young 
spermatids, where it has the form of a very delicate cuticle, but it 
disappears as soon as the spermatozoon begins to be formed, and is 
probably dissolved in the cytoplasm. In the Siphonophora, however, it 
persists for a longer period. 
Dr. Pictet has paid especial attention to the accessory nucleus, which 
appears to be a corpuscle formed for the purpose of eliminating from the 
seminal cell the substances which have become useless to the spermato- 
zoon. It is to be borne in mind that the spermatozoon is a ripe cell, 
which will not give rise to daughter-cells by division. Everything, 
P 2 
