Miscellaneous. 479 



coelomic form, others as an aberrant sporozoarium. The general 

 aspect under which this parasite is actually known has been 

 described by M. Giard, who discovered it in 1876. It consists 

 of ])lasmodial masses of a blackish or violet colour, irregularly 

 applied to the internal face of the test of the sea-urchin and 

 enclosing spherical cysts containing niimerous spores, appendiculate 

 and with falciform corpuscles. Each cyst encloses besides a 

 central spherical mass of tiny crystals of calcic oxalate. 



Before seeking the origin of these cysts, I examined carefully the 

 liquid of the cavities of a great number of sea-urchins, and I 

 discovered in a great number of them monocystid Gregarinidse, 

 solitary or conjugated, free in the liquid. On continuing the 

 investigation I succeeded in finding the various intermediate stages 

 between the phase of young monocystid and the crystalline cysts 

 of Lithocystis ; in fact the gregariuid origin of these cysts was 

 established. 



The free gregarinid is difficult to see, especially when it is young, 

 because it is not common and often concealed in the convolutions 

 of the digestive tube. It is cylindrical in form, attenuated at the 

 poles, and shows a beautiful striated contractile layer, with a large 

 nucleus and a spherical nucleolus. The conjugate forms are easy 

 to see from their size, their extremely active and complicated 

 movements, and their curious method of copulation. The adult 

 gregarinids measure more than I'o millim., so that they are readily 

 distinguishable by the naked eye. In the conjugation, the attach- 

 ment is not made between poles of the same or opposite name, as in 

 the known forms, but by a small surface situate at about equal distance 

 from the two extremities of the individual, as, for example, in 

 Diplozoon paradoxum : this mode of conjugation, so far as I know, 

 has never been observed in the Gregarinidse. When the moment of 

 encystment approaches, the two individuals take on a more massive 

 form and their movements become gradually slower. It is at 

 this period that the crystals are formed which are found later in 

 the ripe cysts. To this end there appear on each individual 

 numerous spherical clear vacuoles, in each of which a single crystal 

 is formed, of the clinorhombic type, which appear to me, so far as 

 microchemical analysis will show, to consist of calcic oxalate. When 

 the encystment is complete, and the divisions of the nucleus and the 

 protoplasm, which are to give origin to spores, begin to be effected, the 

 vacuoles disappear and the crystals unite to form a common sphere in 

 the centre of the cyst. These crystals, which appear at the beginning, 

 in a kind of excretory vacuoles, ought, I think, to be regarded as a 

 veritable excretory product of the gregarinid, a product which, 

 having become useless or even a hindrance to the division of the 

 protoplasm, is separated from the rest of the creature at the 

 moment of reproduction. The presence of this product in the 

 interior of the gregarinid is not at all surprising when one considers 

 that the fluid in the general cavity of the Ecliiiwcardium, contains a 

 large proportion of salts of lime ; it ought to be found in all tlie 

 coelomic gregarinids of Echinodcrms with a calcareous tost — a fact 

 which I have already verified for Spaiaiigus lividus from the 



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