HELK/OA 



741 



hours as a colony, they may separate again without having 

 undergone any discoverable change. 



Under the generic name Actinophrys was formerly ranked the 

 larger but less common Heliozoon. now distinguished as Actino- 

 sphcrrium Eichornii (fig. 574) ; the pseudopodia are longer and 

 more numerous ; there are generally a number instead of one con- 

 tractile vacuole, and there is more than one nucleus. The axis of the 

 pseudopodia may be seen to be clothed with a layer of soft sarcode 

 derived from the super- 

 ficial or cortical zone of 

 the body. Severn! nuclei 

 (v?, n) are usually to be 

 seen imbedded in the 

 protoplasmic mass. The 

 general life-history of 

 this type corresponds 

 with that of the pre- 

 ceding, but its mode of 

 reproduction presents 

 some marked peculiari- 

 ties. In many if not in 

 all cases it commences. 

 as first observed by 

 Kolliker, with the con- 

 jugation of two separate 

 individuals. The binary 

 segmentation is pre- 

 ceded by a withdrawal 

 of the pseudopodia. even 

 their clearly defined 

 axis becoming indistinct 

 and finally disappear- 

 ing ; the body becomes 

 enveloped by a clear 

 gelatinous exudation, 

 which forms a kind of 

 cyst ; and within this 

 the process of binary 



subdivision is repeatedly 



f i ,-i . i " 



performed, until the 



original Single mass is 

 replaced by a sort of 



morula, each spherule of which shows the distinction between the 

 central and cortical regions, the former including a single nucleus, 

 whilst the latter is strengthened by siliceous deposit into a firm 

 investment. After remaining in this state during the winter the 

 young ActinoepJuxria come forth in the spring without this siliceous 

 investment, and gradually grow into the likeness of their parent. 1 



1 On the results of the artificial division of Actinospharium see K. Brandt, Ueber 

 Actinospkcerium Eirhornii, Halle a/S., 1877; Gruber, Bericltte d. Naturf. Ges. zu 

 Freiburg i/B., 18s> ; Nussbaum, Arcli.f. Mikr. A)iat. xxvi. 



FIG. 576. Claihruhna elcqans: A, complete 

 organism; B, swarm-spore showing nucleus, n, 

 and two contractile vesicles near its opposite end. 



