194 Aliscelluneous. 



course of formation and arranged round a central residual mass. 

 This residue is finally reduced in many spores to 2 or 3 granules of 

 strong refractive power, and may even completely disappear at 

 maturity. 



The white crystalline point is formed of crystals belonging to the 

 clinorhombic system, and frequently grouped in macles of great 

 beauty. These crystals are entirely insoluble in acetic acid, but 

 soluble in nitric acid ; they are broken up at the maturity of the 

 cyst, forming at first a sort of network which appears to perform a 

 part analogous to that of the capillitium of the Myxomycetes in the 

 dissemination of the spores. 



As regards the plasmodial masses, their coloration is due to a great 

 nximber of pigment-granules of very unequal dimensions ; the smallest 

 of these are animated by a very brisk Brownian movement. I 

 believe that these granules are obtained by the parasite from the 

 pigment-cells of the urchin. Hofmann has shown that these pig- 

 ment-cells are very abundant in the liquid of the general cavity of 

 the Spatangida). In the mi^jst of these granules we find a prodigi- 

 ous quantity of Amoebfe emitting pseudopodia and agglutinating the 

 grains of pigment. These Amoebae present a nucleus which it is 

 often difficult to see. Although amoeboid cells have been de- 

 scribed in the cavitary- liquid of the urchins, I find it impossible not 

 to admit that the Amoebje in question are genetically related rather 

 to the cysts than to the tissues of the Echinoderm. I regard them 

 as originating from the falciform corpuscles, which lose their form 

 slowly under the microscope : and I believe that by their union and 

 growth these Amosba3 constitute the pigmented plasmodia. It is in- 

 teresting to remember here that M. Balbiani remarked that the 

 Psorospermiae of fishes are in general developed on the course of the 

 blood-vessels, and that their presence causes a considerable diminu- 

 tion of the number of the red globules in the blood of tho«e animals. 



I have found nothing resembling Gregarina?. and the whole of the 

 facts observed lead me to approximate the parasite not to the lower 

 animals but to the lower plants (Myxomycetes and Chytridineae) ; 

 on the other hand, the spores being identical with those described as 

 originating from the cysts of Gregarinae, it may be a question whether 

 the relations of the Psorospermiae to the Gregarinae are not relations 

 of parasitism rather than genetic. 



The presence of the parasite sometimes causes the formation on 

 the inner surface of the test of the urchin of small nodosities, which 

 may perhaps enable us to recognize traces of similar Protista in 

 fossil Spatangidae. 



From the characteristic masses of CT3'^stals I give this parasite the 

 name of Lithocystis; and I dedicate the species to M. Amatus Schnei- 

 der, who has recently studied some analogous productions. 



These researches were made at the laboratory of Wimereux during 

 the months of April and May. — Translated from a separate impres- 

 sion communicated hy the Author. 



