THE SARCODINA 97 



supposed that Arcella, which he found in pairs, were conjugating, and 

 later he held the view that the phenomenon is quite widespread. 

 Holman ('86) observed a large Amoeba surround a small one, the 

 two remained together for some time, and after they separated 

 swarm-spores were formed in each. She regarded this as a possible 

 case of conjugation. A somewhat similar process occurs in Amoeba 

 spatula, although here the smaller individual does not regain its iden- 

 tity, while the larger one appears as before, except for the presence 

 of two nuclei (Penard, 'go). Conjugation is apparently more common 

 among the shelled forms; Penard ('90) says that, although he has 

 met with conjugating animals in almost all of the species studied by 

 him, he cannot cite a single instance where he has seen two animals, 

 at first free, approach each other and fuse. Jickeli ('84) was more 

 fortunate, for he saw two individuals of Difflugia globulosa fuse by 

 their mouth-parts, the union being followed by lively pseudopodial 

 movements. After twenty-four hours one shell appeared transparent, 

 the other dense, while all movements had ceased. When the two shells 

 separated at the end of forty-eight hours, one was empty, its contents 

 having fused with those of the other shell. Gruber ('87) also reports a 

 similar conjugation between two Difflugias. Conjugation has been 

 frequently described in the Heliozoa also, although it is quite possible 

 that many cases of so-called conjugation are only instances of plas- 

 togamy, or fusion of the cell-body, and are not followed by union of 

 the nuclei (karyogamy), as in fertilization. 



Numerous observations might be cited which seem, at first sight, to 

 show that copulation and conjugation, in Heliozoa, are preliminary 

 to reproduction by simple division or by spore-formation, but the evi- 

 dence in most cases is incomplete, and the connection between con- 

 jugation and reproduction is still largely inferential. The ease with 

 which large forms like Actinosphcerium can be artificially reproduced 

 by breaking them into pieces (Foulke, '83) is reason enough to excite 

 caution as to generalizations on the connection between copulation 

 and increase. The phenomenon is, nevertheless, clearly established 

 in at least one form (Actinophrys sol, Schaudinn '96). In this case 

 two free-swimming individuals come together and fuse ; pseudopodia 

 are drawn in, and the double cell sinks to the bottom, where it becomes 

 coated by a cyst of silicious plates. Each of the two as yet ununited 

 nuclei now prepares for division, passing through typical spireme and 

 spindle stages as in Euglypha. Two of the four nuclei which are 

 formed by these divisions round out and become normal nuclei, the 

 others degenerate and finally disappear without playing any further 

 role. The phenomenon recalls in a striking manner the formation 

 of polar bodies among the Metazoa, and obviously represents some 

 form of maturation (Fig. 54). The two functional nuclei now fuse, 



