1885.] 



CLADOCKKA. 



17 



water, the animal at first iuvariably presents itself to the ob- 

 server either in a dorsal or ventral aspect, the strongly diverging 

 antennæ preventing its turning in a lateral position. Not till 

 the antennæ are reflexed or forced back along the sides of 

 the carapace. — a movement, as a rule, performed by the ani- 

 mal after some time spontaneously — is it possible to turn the 

 body over, and thus obtain a lateral view. Often, however, it will 

 soon suddenly again extend its antennæ, and thus instantly 

 reassume its original position. Moreover, when under the micro- 

 scope, the animal curves, as a rule, the free part of its body 

 strongly downward, so as to force it out from the valves, the 

 eye being then often forcibly retracted from the frontal margin. 

 But after a while it generally stops its exertions, remaining quite 

 immobile, and thus admits of being accurately figured with the 

 aid of a camera lucida while still living, any special means for 

 restricting possible movements being superfluous. 



The first specimen of this form appeared in one of my 

 aquaries on the 30th of June, but, at that time, was so very small 

 as to be hardly visible except with the aid of a strong magni- 

 fier. Subsequently, several other specimens developed in the same 

 aquary, and about the middle of July most of the specimens were 

 full-grown and provided with numerous summer-eggs and embryos. 

 At this time, however, I was obliged to break off my observa- 

 tions, having to leave Christiania on a scientific excursion. On 

 my return, late in September, I found this form to have entirely 

 disappeared in the said aquary, its place being tåken up by large 

 shoals of another Australian Cladoceran, Daphnia Lumholtzii, of 

 which I had observed a few young examples only before proceed- 

 ing on my excursion. On the other hand, some few specimens 

 of the same Diaphanosoma had appeared in the largest of my 

 aquaries, along with the Moina to be described in the sequel. 

 But these specimens were of rather inferior size, with but 

 few (rarely more than two) eggs, or embryos, in the matrix. In 

 some of them, also, an incipient production of winter-eggs could 

 be detected; and hence, in all probability, male individuals had 

 now likewise become developed. Meanwhile, I did not succeed 



Vid.-Selsk. Forh. 1885. No. 8. 2 



