724 THE VOYAGE OF H.M.S. CHALLENGER. 



pseudopodia ; but in many species (and probably more or less in all ACANTHARIA) there 

 is recognisable a certain regularity in the disposition of the numerous pseudopodia and 

 of the pores by which they radiate from the capsule. Sometimes these pores are 

 disposed in a regular network of ramified lines, whilst the meshes of this network are 

 devoid of pores ; in other cases they form regular tufts or bushes between the radial 

 spines. Probably in no ACANTHARIA are the pores of the capsule membrane so 

 numerous and so equally distributed throughout as in the SPUMELLARIA ; we may there- 

 fore call the former ACTIPYLEA (in opposition to the latter as PERIPYLEA). 



The Nucleus of the ACANTHARIA is constantly excentric, whilst it is originally 

 constantly central in the SPUMELLARIA. This excentric position is a necessary consequence 

 of the centrogenous development of the radial spines. Probably connected with this' 

 peculiarity is the other, that the nucleus assumes a peculiar, complicated structure, and 

 that in the greater number of ACANTHARIA it becomes cleft very early, and that this cleavage 

 is effected by a peculiar kind of gemmation, first detected and very accurately described 

 by R. Hertwig (compare his Organismus d. Radiol., 1879, pp. 10-24). However, in the 

 young ACANTHARIA the nucleus is constantly simple, and in a certain number of species 

 its cleavage takes place late (as in the greater mimber of SPUMELLARIA). 



The Endoplasm, or the intracapsular sarcode, exhibits in the greater number of 

 ACANTHARIA a more or less distinct radial arrangement ; but this is often concealed by 

 the different enclosed products of the endoplasm oil-globules, vacuoles, red or different 

 coloured pigment-granules, crystals, &c. Often it encloses a variable number of " yellow 

 cells " (becoming green by mineral acids) to be considered as symbiotic xanthellse. 



The Calymma or the jelly- veil, including the central capsule, in the ACANTHARIA is 

 more or less voluminous, and commonly envelops the skeleton perfectly. In its surface 

 is sometimes developed a peculiar network of " supporting fibres." A very peculiar 

 product are the remarkable " Myophrisca " of the Acanthometra, which are wanting 

 in the Acanthophracta; they were first detected by Johannes Miiller, and figured 

 as " Cilien-Kranze," afterwards explained by Hertwig as ".contractile Faden," similar to 

 muscular fibrillse (compare below). 



The Matrix, placed between the calymma and central capsule, in the majority of 

 the ACANTHARIA is a rather thin layer of granular exoplasm. 



The Pseudopodia arising from it are not so numerous as in the SPUMELLARIA, and not 

 so equally disposed over the whole surface. Also their tendency to ramify, anastomose, 

 and form networks seems to be much less developed. Commonly they are simple or 

 little ramified. In many cases (and perhaps everywhere) there may be distinguished 

 two different kinds of pseudopodia : (1) Axopodia, or permanent pseudopodia (with 

 axial filaments?), piercing the wall of the central capsule, and arising from the central 

 mass of endoplasm ; and (2) Collopodia, or variable pseudopodia (without axial filaments), 

 arising outside the capsule from the matrix of extracapsular sarcode or from the 



