468 SUMMARY OF CURRENT RESEARCHES RELATING TO 
period of development the nucleus becomes excentric, and the corpuscles 
of the idiozome increase in number and size, and ultimately fuse together 
to form a little vesicle enclosing a single large granule. The vesicle lies 
within the idiozome. The idiozome then approaches the nucleus and 
its vesicle begins to flatten out until it ultimately envelopes the nucleus 
like a cap ; the remainder of the idiozome meanwhile retreats into the 
cytoplasm. The nuclear cap later becomes the cap of the head of the 
spermatozoon. While these changes have been going on, the cell peri- 
phery has grown out into a slender thread, the rudiment of the future 
tail. With this thread the distal central corpuscle is intimately connected. 
The two central corpuscles then travel inwards towards the nucleus, 
the axial thread travelling inwards with the distal one. At this stage 
the nucleus with its cap projects from the surface of the cell-substance, 
and from the cell-substance a series of fine threads are differentiated, 
which surround the central corpuscles and the axial thread like a 
basketwork. Later these threads become shorter and thicker, and ulti- 
mately unite to form a membrane. The membrane becomes converted 
into a tube which envelopes the tail and constitutes the peculiar tail 
appendage. A little later this disappears in the cytoplasm, and the 
cytoplasm shrivels up to form a ball which is cast oft* by the spermato- 
zoon. The changes undergone by the central corpuscles are exceedingly 
complicated, and cannot be rendered intelligible without figures ; one 
point of special importance is that a part of the distal centrosome forms 
a ring round the axial thread, the ring disappearing before the sperma- 
tozoa reach their full development. 
The second part of the paper consists of a critical comparison of the 
observations of the author and of others on the development of the sperms 
of different animals. As to the part played by the central corpuscles, 
the author believes that their chief function is to connect the motile 
tail with the head, and that both in cell-division and in the sperm they 
play the same part in acting as points of origin for motile threads (cf. 
the movements of the chromosomes in mitosis). He believes further 
that their variations in different animals will be found to be intimately 
connected with the particular form of the sperm. He does not believe 
that the central corpuscles act as centres of force. 
Development of Spermatozoa.* — Dr. J. Nusbaum has investigated 
the process of conversion of the spermatide into the spermatozoon in 
Helix lutescens Ziegl. He finds that the spermatide contains two centro- 
somes, a proximal and a distal, and that the relation of the parts of the 
spermatide to those of the spermatozoon is as follows : — The head of the 
spermatozoon arises from the nuclear chromatin of the spermatide, the 
pointed portion of the head arising from the nuclear corpuscles ; the 
axis of the middle piece of the sperm arises from the proximal centro- 
some, while the envelope of this axis arises from the nuclear fluid 
(karyoparamitome) ; the axial filament of the tail arises from the distal 
centrosome and from the cytoplasm (mitome), while its envelope arises 
from the cytoplasm alone. 
Origin of Spermatozoa.']* — Dr. E. v. Korff gives an account of the 
development of the sperms of Helix pumatia which, so far as it goes, is 
* Anat. Anzeig., xvi. (1899) pp. 171-80 (7 figs.). 
t Arch. Mikr. Anat., liv. (1899) pp. 291-6 (1 pi). 
