1887] Embryology, 7 95 
mentioned is very remarkable. The entodermic cells form a 
solid globular mass, filling up for a time the hinder three-fifths 
of the still nearly solid gastrula. This mass is next subdivided 
into a Sharply circumscribed anterior portion, in which the mastax 
is developed, and a posterior portion, from which the rest of the 
alimentary tract is formed. 
As a result of these elaborate and apparently very successful 
studies, Tessin concludes that the Rotifers are not affiliated very 
closely with the higher Annelids, but, on the one hand, with the 
Turbellaria, and on the other with the Crustacea; with the former 
on account of the well-marked lobes around the blastopore and 
the mode of origin of the mesoderm, and with the latter on ac- 
count of the mode of invagination of the mesoderm at the 
anterior margin of the blastopore, the -development of a post- 
abdomen with a forked tip, the position and fate of the blastopore, 
and the somewhat similar position of the anus in some aberrant 
forms of Crustacea (Cetochilus) In summing up he concludes 
that the Rotifers form a special group, which should be placed 
somewhere between lower worms and Crustacea. i 
The Gestation of Armadilloes.—A very remarkable mode 
The reviewer gives a synopsis of Von Jhering’s arrangement 
of the types or principal modes of reproduction. Two great 
subdivisions are recognized : $ i 
; * Biolog. Centralbl., vi. pp. 532-539 (No. 17, 1886). 
2 It is significant in this AE a that when Mai twins are enveloped in a 
common chorion they are always of the same sex. 
