EECENT RESEAECHES ON THE EADIOLARIA. 159 



Reproduction and Growth. 



The reproductive processes of the Radiolaria have as yet been 

 completely worked out in no individual form, and even the early 

 stages of it have been observed only in Acanthometra and TJialas- 

 sicolla amongst the single forms, and in Sphcerozoum, Collosplicera, 

 and, best of all, in Gollosoum, amongst the compound forms. What 

 has been hitherto observed, however, in these different genera is 

 of so similar a character that it seems reasonable to anticipate 

 the existence of similar first stages in Radiolarians generally. 



The first observation was made by John Miiller in 1856*, who 

 saw inside an Acanthometra (apparently within its capsule) a mass 

 of small Monad-like vesicles in motion, which gave off some very 

 delicate filaments "like those oi Acanthometra.'''' 



In 1858, Schneiderf saw moving vesicles inside the capsule of 

 a Thalassicolla, the vesicles being provided with protruding and 

 retractile processes and also with flagella. 



In 1859, Haeckel + discovered that the content of the capsule of 

 Spheerozoum breaks up into vesicles, which he observed to vibrate* 

 but he did not notice any flagella. He noticed, however, that the 

 several vesicles each contained within it a whetstone-like crys- 

 talline body, such as had been previously found amongst the intra- 

 capsular sarcode of the same species. On this account and on 

 account of its supposed exclusion from the digestive process, 

 Haeckel suspected the central capsule to be the generative organ, 

 as Miiller, for a time, thought the yellow cells might be. 



In the same year he found §, in Acanthometra tetracopa, five 

 small bodies like young Acanthometrce ; but as he found no others 

 in hundreds of AcanthoonetroB, and as they were not observed till 

 after the crushing of the capsule, he suspected that they might 

 have been merely adherent to it and not have come from within it. 



Toung Acanthometrce have the spines only imperfectly deve- 

 lopedll, sometimes only eight, and scarcely perforating the capsule 

 or even being as yet quite within it. 



As to the compound forms, Haeckel believed that their capsules 

 increased not only by fission but also endogenously ; and he also 

 believed that individuals separate themselves and lay the founda- 

 tion of fresh colonies, for he often found single capsules of Sphce- 

 rozoum and Collozoum. He never observed the actual fission of 

 any colony, yet such fission seemed indicated by the beaded (appa- 



* Abhand. d. k. Akad. Berlin, 1858, p. 14. t Milller's ' Archiv,' 1858, p. 41. 

 Radiolarien,' p. 141. § L. c. p. 144. || L. c. pi. xv. fig. 7. 



