186 
the summer months. Thus in the vernal pulse of pala (type only) 
reaching 716,982 on April 24, 1896, 19,056 individuals were para- 
sitized by Bimerium hyalinum Przesm., or by something very 
similar to it, and 30,966 were infested by a fungus-like growth. This 
is about 7 per cent. of the total individuals. Similar though less 
pronounced outbreaks have attended other vernal and autumnal 
pulses. Species of Colacitwm are sometimes found attached to the 
loricee of this species. 
Brachionus pala is exceedingly variable, especially in the matter 
of the development of the posterior spines. Forms without the 
spines (pala type) intergrade, by only slight gradations, into those 
with fully developed spines (var. amphiceros). The angle which 
these spines make with the lorica is also a matter of great variation, 
in preserved material at least. Individuals with the spines at right 
angles to the antero-posterior axis are occasionally seen. The 
species also varies in the matter of the dorsal-ventral curvature of 
the antero-median spines (var. dorcas). Individuals with such 
curved antlers are sometimes provided with posterior spines (var. 
dorcas form spinosus). I have followed Weber (98) in placing 
B. amphiceros Ehrbg., B. dorcas Gosse, and its form spinosus Wierz. 
as varieties of B. pala. They do not, however, all stand upon an 
equal footing. B. amphiceros grades imperceptibly into B. pala, and 
has the same seasonal distribution. B. dorcas and its form 
Spinosus intergrade with each other as do pala and amphiceros, and 
they also exhibit some intergradations with B. pala; but they are 
winter varieties, or at least belong to the colder season, as will 
appear later. Their differentiation in this respect is thus more 
striking than that of B. amphiceros, and makes it probable that we 
have in dorcas a seasonal variety of B. pala. Zacharias (’98) has 
reduced B. pala to a variety of B. amphiceros because in his opinion 
the latter is the more widely distributed form in certain pond waters 
which he examined. This is a criterion which presupposes a wide 
knowledge of distribution and numbers, and, furthermore, a basis 
which can not fail to add to the confusion already existing in this 
genus, since it is hardly to be hoped that it will lead to the same 
conclusion in the hands of different investigators in different regions, 
or even in different seasons and years in the same region. As an 
illustration of the difficulties which might arise I may cite the yearly 
averages of amphiceros and pala in the table on page 182. In three 
