JENNINGS: DEVELOPMENT OF ASPLANCHNA HERRICKII. 87 
PART SECOND.—DISCUSSION OF MATTERS BEARING 
UPON THE MORPHOLOGY OF THE ROTIFERA. 
Our knowledge of the development of the Rotifera is due chiefly to 
the work of Zelinka (91). This author has given a full and careful 
description of the development of Callidina russeola Zel. from the egg to 
the adult form, with a briefer, but still extended, comparative account of 
the development of Melicerta ringens. — Earlier works on the embryol- 
ogy of the Rotifera are due to Salensky (72), Joliet (83), Zacharias 
(84), and Tessin ('86); but all of these works are incomplete and in 
many respeets inaceurate, so that they have been almost completely 
superseded by the work of Zelinka. In diseussing the development of 
Asplanchna I shall therefore restrict myself chiefly to a comparison with 
the results of Zelinka, drawing upon the accounts of other authors only 
where there is special oceasion. 
Since my work has been done primarily from the standpoint of cyto- 
mechanics, and not with regard to the morphology of the Rotifera, it has 
an entirely different aim from that of Zelinka. It thus results nat urally 
that, in giving an account of the bearing of my studies on questions 
relating primarily to rotifer morphology, emphasis must be laid chiefly 
upon the points in which my results differ from those set forth in 
Zelinka’s paper. The plan of my work required a more minute study of 
the eleavage than was demanded for Zelinka's purposes, and as a natural 
rosult I shall be compelled to eriticise his acconnt of the cleavage in 
regard to certain details. Furthermore, it will be necessary to show 
that Zelinka has been incousistent in his aecount with regard to the 
place where the polar cell is formed, and hence is mistaken in his state- 
ment of the axial relations of the egg and embryo in the Rotifera. But 
all these are matters of detail, not affecting in any important way 
Zelinkws general conclusions, and I wish to say at the beginning that I 
fully appreciate the thoroughness and excellence of Zelinka’s researches 
upon this difficult group, and make the criticisms and corrections con- 
tained in the following pages in no spirit of disparagement. 
Asplanchna Herrickii de Guerne, the form upon which my studies have 
been made, is not closely related to any of the species of Rotifera whose 
devolopment has been previously described. Callidina and Melicerta, 
investigated by Zelinka (91), belong respectively to the groups Ddelloidea 
and Rhizota of Hudson and Gosse (86). Rotifer and Philodina, studied 
by Zacharias (81), belong also to the Bdelloidea. Brachionus, investi- 
