288 CLAUS, ON THE 



subject of Nkothoe is the discovery of the male form, which 

 has hitherto escaped observation. The creature, at any rate, 

 regarded by Van Beneden as the male Nicothoe has probably 

 no connection with our species, and perhaps represents 

 another Entomostracon, found accidently associated with the 

 female Nicothoe. It must be confessed that no direct proof 

 of the male nature of the form about to be descril^ed, and 

 which was discovered by Prof. Leuckart on the branchiae of 

 Nicothoe, and submitted to me (in a microscopic preparation) 

 for examination, has been aii'orded by observation of sexual 

 congress, or the discovery of the male organs. Nevertheless, it 

 appeared to agree so completely with the female Nicothoe in 

 all the principal characters, including even the absence of the 

 alseform thoracic appendages, that no doubt can be retained 

 as to their specific identity. But since, according to Bathke^s 

 observations, rudiments of the thoracic ala3 in the female exist 

 even in the earlier stages of development, and, on account of 

 the growth of the sexual organs, constitute an important and 

 never-failing character of the female, and as, moreover, the 

 observed form possesses the full number of somites, and thus 

 represents a perfectly mature sexual condition, it can only be 

 regarded as the male of Nicothoe. 



In the first place, with respect to the segmentation of the 

 female body, which, in its general form, has been suflQciently 

 well described by the writers above cited, I have to remark that, 

 up to the present time, the structure of the head and tliorax 

 has not been rightly understood. That portion of the body 

 which projects free above the ala^form lateral appendages by 

 no means represents the head alone, but is, in fact, consti- 

 tuted of the head together with the first thoracic ring, from 

 which the first pair of bifurcated, swimming-feet arises. The 

 three following somites, therefore, which remain distinct only 

 on the dorsal surface, in the form of three corresponding 

 zones, represent not the three first thoracic somites, but 

 the second, third, and fourth, whose fully jointed feet are 

 attached close to each other, immediately behind the first. 

 Another segment, from protrusions of which, according to 

 Van Beneden, the monstrous alse are constituted, does not 

 in general (uberhaupt) exist. I have fully satisfied myself 

 that the lateral sacs are developed from the ventral and 

 lateral surfaces of all the three free thoracic rings, whose 

 original distinction from each other is recognisable only in the 

 three dorsal zones just mentioned. The last thoracic segment 

 is rudimentary, like the corresponding fifth thoracic ring in 

 Cyclops, and is represented by a narrow zone distinguishable 

 only on the ventral aspect, and from which the single-jointed 



