No. 409.] REVIEWS OF RECENT LITERATURE. 65 
part which are six in number and persist to a much later stage in 
ontogeny. Of these the first gives rise to the cerebellum, and the 
remaining five to the medulla. The brain thus consists of eleven 
neural segments. 
As a suggestion of what might be done, the work of T. B. Pieri 
(Arch. Zool., Exp. III, p. xxix) is interesting. Having shaken the 
sperm of sea-urchins in a bottle of water for one-quarter of an 
hour, he found the sperms apparently dead. When passed through 
a filter the liquid, water and sperm, was added to sea-urchin eggs 
and these developed into many-celled stages. The author would 
fain see here the action of a soluble ferment which he would call 
ovulase ; this truly would be “féconde en consequences biologiques et 
philosophiques." However, he sees clearly that the experiments fail 
in that the filtration did not remove the sperms and that some of the 
sperms may not have been killed. 
The free-swimming copepods of the Woods Holl region have 
been described in the United States Fish Commission Bulletin for 
1899 by Professor W. M. Wheeler. The paper contains accounts of 
thirty species, several of which are new, as well as excellent tables 
for the identification of these crustaceans. 
The peripheral distribution of the cranial and first two spinal 
nerves of the salamander, Spelerpes bilineatus, has been worked 
out by Miss M. A. Bowers. The paper, which is published in 
Vol. XXXVI of the Proceedings of the American Academy of Arts 
and Sciences, is illustrated by four figures in which the nerve com- 
ponents are brought out by appropriate colors. 
Special Bulletin No. 4 from the United States National Museum 
consists of a monograph of the American hydroids belonging to 
the family Plumularidz by Professor C. C. Nutting. The memoir 
includes a general account of the group and descriptions of some 
120 species, nearly half of which are new to science. Itis illustrated 
by thirty-four plates, containing over 300 figures. 
The peculiar trematode, Macraspis elegans Olsson, has been 
studied recently by Jágerskióld (Kg/. Vet-Akad., pp. 197-214, Stock- 
holm, 1899). Good illustrations give the form, which varies greatly 
as between old and young individuals. The entire structure, apr 
cially that of the reproductive system, shows such similarity with 
that of the digenetic trematodes that the author is not inclined to 
Separate the Aspidobothrida so widely from them as has been the 
custom hitherto. 
