146 M. E. Penard's Notes on some Heliozoa. 



to distinguish from the former, and to which the name of 

 eetosarc is given. 



In this brief general description of the Heliozoa we may 

 mention lastly the more or less numerous vacuoles which 

 appear and disappear irregularly in the mass of the 

 plasma, and the more differentiated contractile vesicle, which 

 probably is not deficient in any Heliozoon. This vesicle pre- 

 sents phenomena of diastole and systole, slowly increasing 

 in volume and then suddenly contracting. Frequently we 

 only see one of them ; but I have remarked that even in the 

 species which normally have onlj a single one we may always 

 expect to find individuals which have several ; thus the num- 

 ber of the contractile vesicles, in my opinion, is only of very 

 secondary value in the determination of species. 



I wish at present to treat only of some points in the anatomy 

 of the Heliozoa and of some still imperfectly known pheno- 

 mena in the life of these animals. In fact at Wiesbaden, a 

 locality which has proved to be very rich both in species and 

 individuals, I have had the opportunity of studying most of 

 the forms which have hitherto been described, and my obser- 

 vations have been made upon a number of individuals so con- 

 siderable that I have been able to arrive at conclusions 

 deserving of some interest. 



In the first place I shall say a few words upon the protec- 

 tive covering of certain typical forms. In Actinophrys sol it 

 is the vacuolized eetosarc which performs the part of the enve- 

 lope ; the body is surrounded by a layer of vesicles, which, 

 by their mutual pressure, often form a regular pattern of cells 

 with the walls formed simply of hyaline plasma. In Actino- 

 sphcerium Eichhorni the case is again the same, but the layer 

 of cells is more regular, so that, under a low power, the eeto- 

 sarc appears like a wide clear band traversed by radiating 

 striae, these striae only representing the walls of the cells. 



If now we pass at once from the Actinophrydians to the 

 great family of the Acanthocystidaj we find a very different 

 structure. The central mass of the body is still surrounded 

 by a mucilaginous envelope, but without vacuoles j and this 

 envelope itself seems to be doubled, the narrow inner zone 

 remaining homogeneous and clear, the outer one containing 

 a considerable number of small tangential scales, which are 

 sufficiently close together to lead to the belief in a continuous 

 membrane, or may even overlie one another ; besides these 

 tangential scales we find, immersed in this external zone of 

 the envelope, the bases of the radial spicules to which wc shall 

 refer hereafter. 



