M. F. Plateau on the Freshioater Crustacea of Belgium. 13 



six for the genus Lynceus, and twenty-three for the genus 

 Gypris • and among these last a species which I believe to be 

 new, and for which I propose the name of C. quadripartite,. 



As regards my anatomical and physiological researches, the 

 following are the results which I consider new. 



Gammarus puteanus, Koch, is, as is well known, a singular 

 animal, Avhich lives exclusively in subterranean pieces of water, 

 and its eyes are rudimentary and destitute of pigment. I have 

 made some experiments on the sensibility of the eyes of Gam- 

 marus picteanus • and it appears from these experiments that 

 light hurts them, as is the case in nocturnal animals, and that 

 the Gammarus even flies from diffused light, taking refuge 

 under the shadow of opaque bodies which may be offered to it 

 for this purpose. 



Since the time of Muller the genus Lynceus had never been 

 the subject of any general work. I have taken up the ana- 

 tomical study of these little animals, paying particular atten- 

 tion to the facts neglected by Muller and other authors. In 

 my memoir I pass in review : — 1. The form of the antenna? of 

 the first and second pairs ; the latter do not originate here, as 

 in the Dapliniw^ from the outer sides of the head, but beneath 

 the margin of the beak. 2. The form of the body, properly 

 so called, which includes only seven segments. 3. The struc- 

 ture of the rudimentary eye or black point, and of the true eye. 

 I show that the true eye, contrary to what is stated in this re- 

 spect by Rathke with regard to the Daphnice, is at first repre- 

 sented in the embryo by a pigment-mass supporting a sort of 

 entire nucleus ; the mass and nucleus divide into two distinct 

 parts, and by their subsequent development become reunited 

 by their inner faces. 4. The digestive apparatus : the 

 maxilla? of the Lyncei are triturant, and bear a crown of 

 conical asperities ; the digestive tube is not uniform in the 

 greater part of its extent, but we find in it an oesophagus, a 

 first dilatation into which opens a diverticulum corresponding 

 to the cseca of the Daphmce, a large sac with glandular walls, 

 which I shall call the stomach, a slender intestine forming 

 several convolutions, already represented by Muller, and, 

 finally, a straight large intestine inflated like the colon in man. 

 5. The feet, or respiratory limbs. The limbs of the Lyncei } 

 in addition to the antennary rami, consist of five pairs, which, 

 however, are far from being constructed upon a uniform plan ; 

 they may be divided as follows : — natatory feet with a rudi- 

 mentary respiratory vesicle, and furnished with a flat disk for 

 striking the water ; feet destined to produce a current of water 

 between the valves, also with rudimentary respiratory vesicles, 

 but furnished with long, rigid setae ; and exclusively respira- 



