300 Dr. Pliilip])i on the Hersilia apodiformis. 



at one end a point with an aperture, the membrane forming 

 the envelope being contracted into a narrow chord. The Less 

 developed smaller cases are nearly 2"' long and 1'" broad, and 

 contain about twenty to thirty yellow eggs, which appear to 

 be kidney-shaped when slightly magnified, but when more 

 strongly magnified they already show 1 to 1 J whorls of a 

 shell. The larger egg cases are nearly twice the size,, and the 

 embryos may be very plainly seen. We recognise a regular 

 a of two whorls wound to the right, and two black eyes 

 behind, which have between them a blackish stripe, the intes- 

 tinal canal ; the aperture of the shell is extended beneath, 

 as in Proto, Defrance. I did not succeed in examining the 

 embryo more accurately. The young shell did not dissolve in 

 vinegar, and from this appears to^e of a horny nature. In try- 

 ing to lay bare the little animal by compression, it was com- 

 pletely crushed every time. 



Fig. 8. Eggs of Vermetus gigas, Biv. 



a. A mass of eggs but little developed. 



b. One more developed, in which the embryos are already furnished 



with one whorl and a half of the shell ; both of the natural size. 



c. An embryo strongly magnified, with two perfect whorls of the shell* 



The eyes and the alimentary canal are seen through. 



10. Hersilia* apodiformis, a new Genus of Entomostraca. 



Plate IV. figs. 9, 10, 11. 



On the second of November I found in some sea water two 

 small Crustacea, which at first sight appeared to be similar to 

 Apus, with a long tail and swimming about very briskly. A 

 closer examination proved that they were two pairs in the act 

 of coitus, which I was able to place under the microscope 

 without their separating ; one pair even held together after 

 death ; the tail was the male. They differed in colour ; in one 

 pair the female was perfectly transparent, the male on the 

 contrary coloured with large purplish red moveable points ; in 

 the other pair it was the reverse, the female was so coloured 

 and the male colourless. From this I suppose that the co- 

 lour is only in consequence of the food taken. 



* This name will require to be changed, having been used by Savigny fur 

 a genus of Spiders. 



