166 PROF. ST. aEORQE MIVART ON 



sence of crystals, Hertwig always found in Collozoum one mode of 

 reproduction only in one colony ; and he speculates as to whether 

 there may not be two distinct species which are externally very 

 similar. In support of stich specific distinctness, he notices that 

 the forms which are provided with crystals have rounded capsules, 

 while those without crystals have elongated capsules — differences 

 before noticed by Miiller. Hertwig concludes from all this that 

 the capsule can be no true generative organ. The nuclei act like 

 true physiological nuclei and attract sarcode around them. The 

 swarming is comparable to a very accelerated cell-division, and 

 he compares it with the free-cell formation of botanists. 



In Gollosphcsra and SplKsrozoa, reproduction takes place, as in 

 the Collozoa,w'\t\\ crystals, and each zoospore has a single flagellum. 



Thalassicolla breeds by the contents of the capsule dividing and 

 subdividing according as the nuclei contained within it are few 

 or many. 



When describing the extracapsular sarcode, certain bodies were 

 referred to as " extracapsular bodies," found by Hertwig in Collo-, 

 zoum, and considered by him as perhaps identical with Haeckel's 

 " extracapsulare Oelkugeln"*, and Cienkowski's "zusammen- 

 gedrangte Blaschen"t, in the same species, and as being, more 

 certainly, the same as the " sehr kleine Nester" found by Miiller 

 in Splicerozoum. 



These structures were described by Hertwig J as being peculiar 

 homogeneous bodies, sometimes surrounding the central capsule 

 so as to cover it, but movable and occasionally wandering, through 

 the extracapsular sarcode, from one capsule to another. Of various, 

 often irregular, shapes, and of various sizes, they seem, when 

 fresh, to contain a heap of small fat-spheres ; but nuclei become 

 visible w^hen they are acted on by chromic or acetic acid. They 

 never possess any external, limiting membrane, and their contents 

 seem similar to the contents of an ordinary capsule of Collozoum. 



Hertwig denies, however, that a great resemblance exists be- 

 tween these bodies and the bodies of aggregated nuclei, already 

 described as found within the capsules of Collozoum without crys- 

 tals, the difference being only in shape, and possibly occasioned 

 by the change from an enclosed to a free condition. He is there- 

 fore disposed to regard them as such reproductive masses which 

 have escaped from their ca,psi4e before breaking up into zoospores, 



* ' Eadiolarien,' p. 149, pi. xxxv. fig. 13. 



t Arch. f. mikrosk. Anat. vol. vii. 1871, p. 378, pi. xxix. fig. 29. 



\ Abhancll. k. Akad. Berlin, 1858, p. 5. 



