FORMATION OF THE GERM ‘LAYERS ‘IN THE 
AMPHIPOD MICRODEUTOPUS GRYLLO- 
FPALPA, COSTA: 
CLARA LANGENBECK. 
THE interesting results which Dr. McMurrich obtained from 
a study of the cytogenesis of the isopods led him to suggest to 
me that I should undertake the study of amphipod development 
from the same standpoint. 
This investigation was begun under Dr. McMurrich’s direc- 
tion in the summer of 1893, at the Marine Biological Labora- 
tory, Woods Holl, Mass., was continued there during the two 
following summers, and was completed during my term of the 
Biological Fellowship at Bryn Mawr College, in the winter 
of 1895-96. I wish here to express my thanks to Dr. Mc- 
Murrich, as well as to Dr. Whitman, Director of the Marine 
Biological Laboratory, and to Dr. Morgan, Professor of Zoology, 
Bryn Mawr College, for their kind interest and assistance. 
Up to the present time observations which have been re- 
corded upon the segmentation stages of the amphipod ovum 
have been made only upon the living egg. For a historical 
sketch of the literature I refer the reader to the Monograph 
upon the Amphipods, by Della Valle ('93). The only paper 
upon the subject which has appeared since then was published 
in December of the same year by Bergh ('93), who calls atten- 
tion to the interesting rotation of the embryo upon the egg, 
and points out the necessity of studying the whole cleared egg 
before sectioning it. The paper does not go into detail, being 
intended rather as a suggestion for future work than as an 
exposition of amphipod development. 
My observations were made upon the egg of a small marine 
amphipod, Mzcrodeutopus gryllotalpa Costa, which lives in 
shallow wateramong decaying seaweed. This species is widely 
distributed, being found on the coast of New England as well 
