34 



G. 0. SARS. 



[No. 8. 



ture exactly with those of M. brachiata, the zoospermes being 

 likewise of a similar character. 



Bespecting colour, both the male and female are, as a rule, 

 highly pellucid, almost hyaline, having however, invariably, along 

 the ventral side of the intestine, a more or less distinct rosy or 

 violet tinge. In gravid females, the prodigiously expanded dorsal 

 part of the carapace often exhibits a faint yellowish tinge, the 

 embryos occurring of a bluish-grey. In most specimens, numerous 

 strongly refracting oil-globules, belonging to the so-called adipose 

 tissue, are dispersed along the ventral face of the body. being 

 especially numerous within the tail, where they occur on both 

 sides of the terminal section of the intestine (see Pl. 6, fig. 1). 

 The recently developed ephippium exhibits an opaque brownish- 

 red colour. 



Observations. — Individuals belonging to the summer- 

 generations move through the water with comparative rapidity 

 in a clearly jumping manner, their bodies retaining a some- 

 what prone attitude. True, the movements of gravid females be- 

 come to a certain extent encumbered by the heavy burden of 

 embryos, but are yet sufficiently vigorous to render it rather 

 difficult to catch them with an ordinary dipping-tube. In the 

 latter part of the summer and autumn, these animals become 

 much less agile, keeping mostly near the bottom of the aquary, 

 though moving ab out in the same jumping manner as before. 



The present form made its appearance in most of my aquaries 

 at about the same time, viz., in the first days of June, a very 

 few individuals only having at first been observed. Meanwhile 

 they rapidly increased, and, when full-grown, they continued multi- 

 plying to such a remarkable extent, that in the course of a few 

 weeks, shoals of these little creatures literally filled up the 

 aquaries. To prevent their choking out, so to speak, all the other 

 Cladocera, I was obliged on several occasions to remove a conside- 

 rable number of the individuals from the smaller aquaries, whereas 

 in my largest aquary I left the animals to multiply undisturbed. 

 On returning from my excursion, I found this aquary filled up with 

 immense swarms of this form, so as to give quite a turbid aspect 



