REPORT ON THE RADIOLARIA. CXXXvii 



social central capsules by gemmation and by cell-division, it would appear that the 

 capsules produced by the former method afterwards produce anisospores, whilst those 

 in the latter way yield isospores ( 216). 



The gemniules or capsular buds of the Polycyttaria were first accurately described by Eichard 

 Hertwig (L. K 26, pp. 37-39), under the name " extracapsular bodies," and their significance rightly 

 indicated ; earlier observers had incidentally mentioned and figured them, but had not seen their 

 origin from the central capsule. Quite recently Karl Brandt has given a very painstaking account 

 of them in the different Polycyttarian genera (L. K 52, pp. 179-198). In the Monocyttaria such 

 a formation of buds has not yet been observed. The basal lobes of the central capsule, which occur 

 in many NASSELLARIA, are not buds, but simple processes of the capsule, due to its protrusion 

 through the collar pores of the cortinar septum ( 55). 



215. Sporification. Asexual reproduction by the formation of movable flagellate 

 spores has been hitherto observed only in a very small number of genera ; but since these 

 belong to very different groups, and since the comparative morphology of the capsule 

 appears to be similar throughout as regards the structure and development of its con- 

 tents, it may be safely assumed that this kind of reproduction occurs quite generally in 

 the Radiolaria. In all cases it is the contents of the central capsule, from which the 

 swarm-spores are formed, both nucleus and endoplasm taking an equal share in the 

 process ; in all cases the spores produced are very numerous, small, ovoid or reniform, 

 and have one or two very long slender flagella at one extremity (see 141, 142). 

 Since the whole contents of the mature central capsule are used up in the formation of 

 these flagellate zoospores, it discharges the function of a sporangium. The division of 

 the simple primary nucleus into numerous small nuclei, which usually (serotinous 

 Radiolaria) takes place only shortly before sporification, but sometimes (precocious 

 Eadiolaria, 63) happens very early, is the commencement of the often repeated 

 process of nuclear division, which terminates with the production of a very large 

 number of small spore-nuclei. The nucleolus often divides very peculiarly ( 69, C). 

 Each spore nucleus becomes surrounded by a portion of endoplasm and usually receives 

 in addition one or more fatty granules, and sometimes also a small crystal (hence the 

 " crystal-spores "). The size of the flagellate zoospores which emerge from the ruptured 

 central capsule and swim freely in the water by means of their flagellum, varies 

 generally between 0'004 and O'OOS mm. The extracapsulum is not directly concerned 

 in the sporification, but undergoes degeneration during the process and perishes at its 

 conclusion. 



The first complete and detailed observations on the formation of spores in the Eadiolaria were 

 published by Cienkowski in 1871 and related to two genera of Polycyttaria, the skeletonless 

 Collozoum and the spherical-shelled Collosphcera (L. N 22, p. 372, Taf. xxix.), These were 

 subsequently continued and supplemented by B. Hertwig (1876, L. E". 26, pp. 26-42, and L. N. 33 

 p. 129), and a general summary of these results has been given by Biitschli (L. N". 41, pp. 449^155). 



(ZOOL. CHALL. EXP. PART XL. 1887.) 



