156 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
winding. The mesonephros shows a glandular sac, the pronephros none. 
The mesonephros consists of numerous external funnels metamerically 
arranged ; the pronephros is sporadically disposed, without relation to 
segments. In segments with pronephros there is also mesonephros ; both 
occur together. The system differs from that of Amia and Acipenser in 
many ways, e. g. in the number of external fnnnels, in having a straight 
pronephric duct, in the union of the pronephric ducts in a cloaca, in 
there being no transitional area between pronephros and mesonephros. 
Spermatogenesis of Selachians.* — M. A. Sabatier, finding that not- 
withstanding previous researches many parts of this subject remain 
obscure, has made a series of fresh observations on the lower surface 
of the testicle of Scyllium catulus. There is a longitudinal band of 
germinal tissue, formed of flat nuclei situated in a reticulated proto- 
plasm. At certain points of this band the nuclei multiply by amitosis ; 
they then grow and form large lenticular masses. Each of these groups 
forms a nest of germs, and will be the origin of a testicular ampulla. 
Often one of the nuclei very early grows much larger than the others, 
and it is this which has been wrongly considered as a female cell of the 
testicle. Each nest of germs grows, and there is formed at the centre 
of the protoplasm a lacuna which increases in size and becomes the 
central cavity of the ampulla. The nuclei or germs commence to divide, 
and arrange themselves in a layer which is applied to the membranous 
envelope of the ampulla. At the same time some of them may acquire a 
proper cellular body. Further changes occur, and all the cells enclosed 
in the ampulla become protospermatoblasts, which are similar to one 
another and have the same value and the same destination. Each divides 
into two smaller cells — the deuto-spermatoblasts, which in their turn 
divide and become trito-spermatoblasts. Other elements appear in the 
ampulla which are altogether foreign to the spermatoblasts already 
formed. They represent the point of departure of the future generation 
of spermatoblasts and spermatozoa. Other difficulties in the spermato- 
genesis of Selachians remain, which the author hopes to resolve. 
Development of Teeth in Teleostei.f — Miss Albertina Carlsson has 
studied this in Salmo salar , Cottus quadricornis, Abramis brama , and 
many other Teleosteans. The following conclusions are reached : — An 
enamel ridge of considerable breadth extends uninterruptedly along the 
whole length of the tooth-bearing bones ; the first hints of teeth are 
seen in the elongation of cells at the base of the ridge ; the teeth do not 
develop in a continuous series, but new ones appear from the unexhausted 
ridge between those which have already been formed ; the ridge usually 
persists throughout life, but may be absorbed on the middle part of the 
jaw between the teeth, as in the pike ; the germs of replacing teeth arise 
either from the base or from the lingual side of the ridge ; sometimes 
there are more teeth or rudiments of teeth in the young than in the 
adult ; the constriction from the ridge is late of being effected, and there 
is no relation between the formation of dentine and the ossification of 
the tooth-bearing bones. 
Endocardium of Bony Fishes, f — Mr. A. T. Holbrook has made a 
special study of the Cod and some allied fishes, and finds that their 
* Comptes Rendus, cxx. (1895) pp. 47-50. 
f Zool. Jakrb. (Abth. Anat. Ontog.), viii. (1894) pp. 216-44 (2 pis., 2 figs.). 
% Bull. Mus. Comp. Zool., xxv. (1894) pp. 79-97 (5 pis.). 
