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BIOLOGY OF THE PROTOZOA 



in the protoplasm. The cell then divides into as many daughter 

 cysts as there are nuclei and these Hertwig calls cystospores No. 1, 

 each of which secretes a gelatinous envelope about itself. The 

 nucleus then divides by mitosis followed by division of the cell into 

 two daughter cells which he calls cytospores No. 2. The nuclei of 

 the latter undergo two successive "maturation" divisions resulting 

 in one pronucleus and two "polar bodies" in each (Fig. 156), the 

 latter degenerating and disappearing. The two cytospores of 

 the second order now unite again, reforming cytospores No. 1 

 and fertilization is completed by fusion of the pronuclei. Belaf 

 quite recently (1922) has given a more complete description of 



Fig. 156. — Actinosphaerium eichhornii. A, two gametes ("cytospores No. 2") 

 resulting from the division of the same mother-cell; B, both "polar bodies" are 

 formed in the right gamete, the second one forming in the left gamete; C, the cell 

 bodies of the gametes have fused, and the nuclei are fusing; D, young organism leav- 

 ing cyst; p, p 1 , p 2 , " polar bodies. " (After Hertwig.) 



the process in the allied form Actinophrys sol. The individuals 

 draw in their pseudopodia, ordinary vegetative division of the 

 nucleus follows, and the cell divides into two. By this division 

 which Belaf terms the "progarnous" division, the two gametes 

 are formed and after each of them has undergone two meiotic 

 divisions of the nuclei they reunite to form the zygote. One of 

 them anticipates the other in these divisions and develops a pseudo- 

 podial process which the other lacks. By this process the first 

 fusion of the two cells takes place. The original cell thus is a 

 gamont and the fusing gametes are sister cells, one of which shows 

 an incipient sex difference in its precocious activity and by its 

 pseudopodium-like process. (Fig. 142, p. 27S.) There are 44 



