73 
Crvptomonas ovata Ehrbg.*—Average number, 121,154. This 
species has been recorded principally in the autumnal or hiemal 
plankton. It escapes through the silk net readily, and was rarely 
found in collections of earlier years. In 1895 it occurred from July 
till the last of October, and in 1898 was common in the December 
plankton. 
Dinobryon sertularia Ehrbg.—Like most typical planktonts, 
Dinobryon is an exceedingly variable organism, and the varia- 
tion finds its expression in the form and proportions of the 
lorice and in their arrangement and continuity in colonies. 
Divergences from described and figured species are thus at once 
apparent, and they have been utilized by systematists, notably by 
Lemmermann (’00) and by Brunnthaler (’01) as the basis for the 
establishment of a large number of new species. The validity of 
these species, in my opinion, must rest ultimately upon careful 
experimental evidence of their present mutual genetic independence 
under normal conditions of growth. From my own observations 
upon large numbers of colonies and individuals distributed through- 
out the range of their seasonal recurrence in six years in our waters, 
I am inclined to regard all as belonging to a single species, and the 
different types as mere growth varieties. The rapidity of growth 
and the age of the individual or of the colony are, I believe, impor- 
tant factors in the determination of the form of the lorica, and its 
various forms are therefore not of specific value, but rather of 
physiological significance. It is a simple matter to find individuals, 
or even colonies, conforming to the descriptions of the several 
species, but it is not so easy to refer all individuals and all colonies 
to the described types. They intergrade—nay, more, two, or even 
more, ‘‘species” are not infrequently combined in the same colony. 
I have never found all the forms in a single colony, but such com- 
binations as angulatum-divergens, divergens-angulatum-stipitatum, 
sertularia-angulatum, and sertularia-undulatum have been observed 
by me. These combinations are most frequent in large colonies, 
and, indeed, the number of “species” in a colony is apparently a 
function of its size. The slender growing tips are wont to assume 
the stipitatum type of lorica and colony, and the older lorice at the 
base to conform to that of sertularia, divergens, or angulatum. 
Small colonies as a rule belong to a single “species.’’ These com- 
binations are generally most evident during the maximum period 
