354 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
with the germinal vesicle ; it is probably identical with the centrosome 
which remains in the ovum after the last division of the germ-cell. In 
ova of plaice and flounder it moves to the inner border of the yolk-layer, 
and becomes surrounded with yolk. In Syngnathus acus there are often 
two or more vitelline nuclei in one ovum. 
The germinal vesicle in Teleostean ova shows at first a single large 
nucleolus, a nuclear network, and a membrane. At the next stage the 
vesicle is larger, and there are several peripheral nucleoli ; in still larger 
ova the nucleoli are still peripheral, but there is a central region with 
separate feathery fibrils, the centrosomes of Riickert. After the forma- 
tion of yolk has begun, the nucleoli are found around and among the 
central fibrils ; and in the turbot there are hints that the substance of the 
nucleoli is absorbed into the central fibrils to form the chromosomes of 
the polar mitoses. 
Development of Spermatozoa in Salamander.* — Dr. F. Meves has 
reinvestigated the much studied development of the spermatozoon in 
Salamandra maculosa. He attended particularly to the role of the central 
corpuscle and the sphere in the formation of the spermatozoon. That 
there is some relation between the middle part of the spermatozoon and 
the central corpuscle has been quite clear for several years. For in 
numerous cases it has been shown that after the spermatozoon enters the 
ovum, a radiate system develops around the middle part. From this the 
inference has been drawn that the middle part of the spermatozoon con- 
tained the centrosome. What Meves claims to have proved is that the 
middle part is formed wholly of centrosome-substance. 
Spermatogenesis in Selachians.^ — Prof. Armand Sabatier has pub- 
lished a lengthy memoir on the spermatogenesis of Selachians, as ex- 
hibited by Scyllium, Acanthias , and Raja. He compares his results 
throughout with those obtained in his study of Crustaceans. 
The origin of the germ-cells is the same in the two cases. They 
occur in groups or nests of nuclei lying in a plasmodium. These primary 
nests are formed by the direct division of the nuclei of the germinal 
connective tissue. Secondary nests are formed by the direct division 
of flattened nuclei contained in the connective membrane of the acinus 
or testicular cul-de-sac. 
The direct division occurs by pulverisation of the nuclein and by 
cleavage. The undivided protoplasm is disorganised. 
The nuclear germs are transformed into protospermatoblasts, each 
acquiring a zone of protoplasm. By indirect division the protosperma- 
toblasts give rise to deutospermatoblasts, and these to tritospermato- 
blasts. There are thus two successive mitoses. 
The head of the spermatozoid and its cap arise from the nucleus, 
which is differentiated in two directions. The middle part and caudal 
filament of the spermatozoid arise from the reticulate protoplasm of the 
tritospermatoblast, but there is in this some “ nuclein-dust,” and at the 
posterior end of the middle part there is a special “ caudal granule.” 
There is, of course, in this long memoir, much more than we have 
been able to summarise ; we have merely noted some of the essential 
points. 
* Arch. f. Mikr. Anat., 1. (1897) pp. 110-41 (2 pis.), 
f Mem. Acad. Montpellier, ii. (1896) pp. 53-238 (9 pis.). 
