M. E. Penard's Notes on some Heliozoa. 145 



their near Amoebiform relatives the tendency towards per- 

 fection is in general directed to the acquisition of a rigid 

 capsule open at one point to allow the passage of the pseudo- 

 podia, as is seen in the carapaces of the Difflugice, Arcellce, 

 Euglyphce, &c, in the Heliozoa we may say that this ten- 

 dency has led towards the possession of a coat of mail sur- 

 rounding the whole body, and from which issue in all 

 directions long radiating pseudopodia. 



The external envelope, however, in some of them still 

 consists only of a thick layer of hyaline plasma, which, in 

 the Actinophrydians, is marked by large vacuoles ; in others 

 (Lithocolla) this hyaline layer is covered with stones derived 

 from the medium in which the animal lives ; in the Clath.ru- 

 lince we find an elegant solid trellis-work, formed throughout 

 by the individual and pierced on all sides ; but in the 

 majority of the species we meet with a true coat of mail, the 

 mobile elements of which, siliceous scales and spicules, are 

 buried in the external mucilaginous layer which has just been 

 mentioned. 



The pseudopodia are always remarkable for their fineness, 

 their rigidity, and their length ; in this respect they differ 

 at the first glance from those of the Amoeban Rhizopods, 

 whether naked or testaceous, although in some of the latter 

 (Euglypha, Trinema, Cyphoderia, &c.) they may also be 

 very long, very fine, and comparatively rigid. 



All the true Heliozoa have at least one nucleus, sometimes 

 two, or even more, but in general unity is the rule ; Actino- 

 sphairium Etchhornu, on the other hand, constantly contains 

 a considerable number, up to one hundred or more. 



This nucleus likewise always possesses what has been 

 called a vesicular structure, which also occurs among the 

 Amcebas ; passing from the centre towards the periphery, it 

 consists of a voluminous central body, surrounded by a thicker 

 or thinner zone of hyaline substance (the nuclear fluid), liquid 

 in appearance, and in its turn bounded by a true nuclear mem- 

 brane, rather thick in the Actinophrydians and very delicate 

 in the other Heliozoa. As to the central mass of the nucleus, 

 generally regarded as the nucleolus, it is most frequently 

 simple ; but sometimes we find it divided into several frag- 

 ments immersed in the nuclear fluid. 



The nucleus, taken as a whole, is central in some species, 

 excentric in the majority, but it always belongs nevertheless 

 to that part of the plasma which has been called endosarc, to 

 distinguish it from a generally less homogeneous, more 

 granular zone, which, however, is often absent or impossible 



