382 Heterogenetic Development in Diaptomus, [April, 
stages in adult Cyclopidæ. I am now able to set the matterat 
rest with reference to these two forms at least. Having had — 
occasion to collect fresh-water animals through the entire length 
of the Mississippi valley from Lake Superior to the Gulf of Mex- 
ico, many hundreds of specimens of Diaptomus have been exam- 
ined in the most diverse localities. If it were permissible to 
establish a species upon slight variations in structure, numbers of 
them might be distinguished. However the following facts debar 
me from attempting it: At Decatur, Ky., a series of small pools : 
in various stages of stagnation, furnished an opportunity for study- 
ing the variations due to age and conditions of the water. | 
It is remarkable that in such small bodies of water only one : 
stage may be present in one, while the next, a few feet away, may : 
offer another. i : 
In the same localities the various stages of a Phyllopod could ! 
be studied in the same way. ie 
The normal D. castor, like Minnesota specimens in its various : 
stages, occurs in some pools, in others, a few steps away, 0%% she : 
a larger form, at a glance distinguishable from the above by i | 
short antennz and stylets, and the structure of the fifth ee i 
was, however, struck by the fact that all these specimens xe = 
mature (though nearly as large as D. giganteus), and w 
panied by the adult stages. Figs. 1, 2, 3 and 9, Plate V a 
some of the peculiarities of the normal D. castor; 14 and 9% 6 and | 
the effect of senility on fifth feet and antenne. Figs 4, 50°" 
9 show the corresponding parts in the enlarged form. a n 
Further study showed me that the difference distinguish W a 
second from the first forms, saving the compact build of hes 
mer, are just those found in young of castor. It pe he 
remained to find the specimens in the process of molting ™ * 
combined characters of both (Fig. 8) to convince one w 
larged form is really identical with casior, but by favorable one 
stances enormously developed. ; veacheh 
Differentiation takes place before the mature stage !S argel 
the same way that tadpoles wintered over are greatly enl Alabame 
I have found the typical D. sanguineus of Forbes ™ the com | 
This form has some peculiarities to distinguish it fou 
mon var. of D. castor.. d 
In view of the facts now known regarding the develop! 
Diaptomus, we may safely say that D. stagnalis Forbes, 
js an | 
