No. 401.) REVIEWS OF RECENT LITERATURE. 441 
*'To sum up the whole matter in a single sentence: It is held 
that bird migration is a habit evolved by education and inheritance 
which owe their origin and perpetuation to winter with its failure of 
food." W. E. R. 
Ovogenesis in Tunicates. — Dr. F. W. Bancroft has published 
(Bulletin of the Mus. of Comp. Zoól., Vol. XXXV, No. 4, 1899) an 
extended account of his studies on the ovogenesis of Distaplia 
occidentalis. 
In general, the development of the gonads and their ducts re- 
sembles that found in Perephora, Clavelina, and Ciona. 
The most significant difference consists in the fact that the funda- 
ment of the ovotestis is present in the youngest stages in Distaplia, 
whereas in the other species it appears quite late in ontogeny. 
To the question which type of ovary is more primitive, that 
represented by Clavelina, where there are two separate germinative 
epithelia, or that found in Distaplia with but a single such epithe- 
lium, the author is inclined to give the distinction to the Distaplia 
type, since here it occurs in a smaller and simpler species, and is 
itself simpler. 
Dr. Bancroft goes at length into the question of the origin and 
fate of the test cells, discussing the whole matter in the light of the 
more recent statements by Davidoff and Salensky, based on their 
observations on Distaplia magnilarva. He does not confirm the 
results of these authors, and as his studies pertained to a species 
very closely related to the one studied by them; and, furthermore, 
as he had the opportunity, through the great courtesy of Professor 
Salensky, to examine slides of D. magnilarva, it would seem that his 
critical findings should be conclusive on this much discussed problem. 
The function of these cells, the author believes, is to furnish 
.nutriment to the growing ovum. He concludes that they are par- 
ticularly active in this capacity in the early stages of the growth of 
the ovum, while the nucleus exerts its principal activity in the later 
stages in converting this nutritive material into yolk. 
The germinative vesicle diminishes in size gradually and continu- 
ously with the increase in quantity of yolk in the ovum. Wir 
Reproduction of Amæba. — In addition to the common and recur- 
ring bipartite division of Amada proteus, Scheel’ has described a 
1 Scheel, C. Beitráge zur Fortpflanzung der Ameeben, Festschrift zum sieben- 
sigsten Geburtstag von Carl von Kupffer, pp. 569-580, Pl. LI. Jena, 1899. 
