228 



THE PROTOZOA 



that they arise in the cytoplasm independently of the nuclei ; but their 

 rejection by the animal is more in favour of the view that they are waste- 

 products of the metabolism (Veley). It is not clear what is the role of the 

 bacteria, whether they are parasites or symbionts. 



Petomyxa reproduces itself by simple fission or by formation of gametes. 

 The sexual process, according to Bott, begins with extrusion of chromatin 

 from the nuclei into the cytoplasm to form chiomidia, which may take place 

 so actively that sometimes the nuclei break up altogether. A similar extrusion 

 of chromidia may take place as a purely regulative process under certain 

 conditions, such as starvation ; -but the vegetative chromidia formed in 'this 

 way, and absorbed ultimately in the cytoplasm, must be distinguished from 



generative chromidia produced 

 as a preliminary to gamete- 

 formation. From the genera- 

 tive chromidia secondary nuclei 

 of vesicular structure arise, 

 which, after elimination of 

 chromatin followed by reduc- 

 tion (see p. 150, supra), 

 become the gamete-nuclei. The 

 gametes arise as spherical in- 

 ternal buds, each with a single 

 nucleus, to the number of 100 

 or more, and are extruded 

 when fully formed, causing 

 the parent-individual to break 

 up completely. Each free 

 gamete is Heliozoon-like, with 

 slender, radiating pseudopodia ; 

 they copulate in pairs, and the 

 zygote grows into a young 

 Pdomyxa, either directly or 

 after a resting period in an 

 encysted condition. 



The genus Paramceba (Fig. 

 49) was founded by Schaudinn 

 (81) for the species P. eilhardi 

 discovered by him in a marine 

 aquarium in Berlin.* In the 

 adult stage the animal occurs 

 as an amoeba, from 10 to 90 /* 

 in diameter, of rather flattened 

 form and with lobose pseudo- 



FIG. 92. Portion of a section through the body 

 of Pdomyxa. N., Nucleus ; r.b., refringent 

 bodies ; 6., bacteria on th6 refringent bodies ; 

 s., sand and debris in the protoplasm. After 

 Gould. 



podia. It contains a single 

 nucleus, and near it a peculiar 

 body, the " Nebenkern " of 

 Schaudinn (see p. 95). In 



this phase the amoeba multiplies by binary fission accompanied by 

 division both of nucleus and Nebenkern. It also becomes encysted and 

 goes through a process of multiple fission, which shows three stages ; in the 

 first the Nebenkern multiplies by repeated division, the nucleus remaining 

 unchanged ; in the second the nucleus divides repeatedly to form as many 

 small nuclei as there are Nebenkerne present, and each nucleus attaches itself 

 to a Nebenkern ; in the third the protoplasmic body undergoes radial super- 

 ficial cleavage into a number of cells, each containing a nucleus and a Neben- 

 kern. Each of the cells thus formed becomes a swarm-spore with two flagella. 



* The amoeba from the human intestine described by Craig under the name 

 Paramceba hominia certainly does not belong to this genus. See Doflein (7), 

 pp. 602, 603. 



