THE RADIOLAR1A 143 



According to the colony under consideration so will these nuclei 

 belong either to the microspore or megaspore. In the former the 

 chromatin is disposed in stout granules and thick strands, in the 

 latter in much smaller quantity. In other respects the colony 

 behaves precisely as in the formation of isospores. 



In the Sphaerozoidae the formation of heterospores takes place 

 both in small, apparently young, colonies that bear extracapsular 

 bodies and also from full-grown vegetative colonies. In both cases 

 many of the nuclei become segregated and differentiated, the endo- 

 plasm in which they lie acquires distinctive characters, and the 

 groups so formed are separated by undifferentiated plasma and 

 nuclei (Fig. 25, B). The oil-globule becomes subdivided into a grape- 

 like mass, which ultimately splits up into minute granules, and 

 these are collected around the specialised nuclei. In the case of 

 colonies bearing extracapsular bodies the whole of this bud becomes 

 transformed into megaspores, the contents of the central capsule 

 becoming microspores. In older colonies the endoplasm is con- 

 verted into a vast number of portions, in each of which the differ- 

 entiated nuclei are aggregated. These nuclei are, however, not all 

 of one kind. Each collection is either meganucleate or micro- 

 nucleate, and accordingly stains feebly or strongly. The contents 

 of the capsule now becomes resolved into biflagellated megaspores 

 and microspores, the ectoplasm degenerates and collapses, the 

 central capsule deliquesces, and the spores become disseminated. 



Little is as yet known as to the formation of isospores and 

 heterospores in other Radiolaria. In Acanthochiasma rubescens 

 (Acantharia) Brandt records the early development of two kinds of 

 bodies one with crystalloid inclusions, the other with lobulated 

 masses of fat. The same observer has described the active spores 

 of Xiphacantha alata and Acanthometra sicula. Two kinds of spores 

 occur in these Acantharia (Fig. 26, A, B). Both are minute 

 (*004 mm. long), and provided with three cilia, which spring from 

 the two poles of the spheroidal or pear-shaped body, but they differ 

 in that the spores of any one individual either contain a minute 

 crystal and few granules or many granules but no crystal. Both 

 are provided with a starch-grain (see pp. 128), and traces of the 

 yellow cells of the parent occur in the granular variety. It seems 

 highly probable, therefore, that crystal-bearing isospores and granular 

 heterospores occur in this sub-class as in the Spumellaria ; but 

 although the results of more recent expeditions have extended very 

 largely the number of Acantharia in which the early development 

 of spores has been shown to occur, the free spores have not been 

 again noticed; nor do we possess any exact observations on the 

 flagellated bodies that have occasionally been seen in Nassellaria 

 and Phaeodaria. 



