MICROSCOPICAL STUDIES. 15 



individual members, at a certain period, break up into innumerable 

 tiny spores ; these spores may be of two distinct series. Thus one 

 colony may give rise to spores all of the same size, isospores, while 

 another may give rise by another method to spores of two sizes 

 (anisospores). The former are probably asexual ; the latter sexual, 

 giving a typical alternation of generation. Both forms are produced 

 within the central capsule. In the formation of isospores, the nuclei 

 of the parent multiply by fission and scatter throughout the capsular 

 protoplasm ; each nucleus appropriates a certain amount of protoplasm, 

 and a minute crystal, and receives several tiny oil globules from the 

 breaking up of the great oil globule. When ripe, each of these 

 masses assumes a pear-shaped form, with the nucleus at the narrow 

 end, whence proceed two flagella which propel the spore through the 

 water, when liberated by the breaking down of the capsular membrane 

 and when disintegration of the extra-capsular matter takes place. 



Anisospores arise also from the multiplication of the mother- 

 nuclei, but the mode is somewhat different. Within the same 

 individual, two well-marked sizes occur ; the larger are termed 

 macrospores, the smaller microspores, and they escape in the same 

 way as do the isospores. Analogy suggests that in these macro- and 

 microspores we have a sexual stage, but the conjugation of these two 

 bodies, which is required to prove this theory, has not been observed. 

 The shajje of both forms of anisospores is reniform (kidney-shaped) ; 

 they are propelled either by one or by two flagella. Isospores and 

 anisospores alike give rise to an ordinary Radiolarian having the 

 typical structure. This by fission of the central capsule repeated 

 frequently, and by gemmation also (?), produces the colonial mass we 

 have before us. Then when the full of adult life is reached, the 

 intra-capsular protoplasm breaks up into either iso- or anisospores. 

 The Life-cycle of such a Radiolarian can be tabulated thus : — 



1. Isospore (asexual spore). 



2. Young Radiolarian individual. 



3. Colony (produced by fission and gemmation). 



4. Anisospores = macrospores, and microspores (Sexual spores) (?). 



5. Conjugation of macro- with microspore (?). 



6. Young Radiolarian individual. 



7. Colony. 



8. Isospore (asexual spore). 



Stage 4 may not necessarily alternate with stage 8 ; indeed it is 

 probable, by analogy, that under favourable life-conditions, the forma- 

 tion of anisospores seldom occurs — many repetitions of isospore 

 generations taking place before one of the anisospore stages recurs. 

 The latter probably occurs when new vigour requires to be infused 



