PROTOZOAN GERM PLASM 577 



In A reel I a, therefore, as in Polystomella, there is a definite germinal 

 protoplasm composed essentially of chromatin which gives rise to new 

 cycles of organisms, while a portion of the original organism, including 

 the primary nucleus and a quantity of protoplasm, degenerates and dies. 

 We can speak of germinal and somatic protoplasm in these cases, and 

 with equal right in all of the 

 thousands of allied species of 

 protozoa, as well as in the case of 

 any higher animal. 



A still more interesting case 

 of specific germ-plasm forma- \^J^^J HP -f<-^\ -^ /srj 

 tion is given by a type of x^'jpf '•/ ',^^$& 



Gregarine belonging to a group FlG u After Elpetiewsky 



of parasitic Sporozoa. In all 



of the Gregarines there is a segregation of the germ plasm and a 

 residual somatic protoplasm which degenerates and dies a somatic death. 

 One of the most striking illustrations of this type is the case of Ophryo- 

 cystis mesnili, a parasite of beetles. Unlike the cases cited above,, 

 most of the gregarines do not reproduce asexually. Ophryocystis, how- 

 ever, is one of the exceptions to the rule, the individuals reproducing by 

 simple division until the protoplasm becomes mature, when, as in 

 Paramecium, two cells come together in conjugation. The single- 

 nucleus of each cell divides and one of the products becomes a 

 " somatic " nucleus, to use Leger's term, while the other daughter 

 nucleus in each cell divides again (Fig. 12, A-G). One of these cor- 

 responds to a polar body in the metazoon egg, the other is the gamete,. 

 or germ, nucleus. In each cell this nucleus collects about itself, pos- 

 sibly through the secretion of nuclear material which transforms the 

 surrounding stuff, a denser zone of protoplasm, which, with the nucleus,, 

 forms a gamete within the body of the parent cell. The two gametes 

 thus formed fuse while in the space which their formation has left in 

 the parent somatic, or nurse cells. The latter ultimately wither up 

 and die. After union of the two gametes, the sporoblast gives rise to- 

 eight germs or sporozoites, each capable of developing into an ordinary 

 vegetative form when under the proper conditions of environment 

 (Fig. 12, H-N). 



Here in Gregarines, therefore, as in rhizopods, we see a clearly 

 defined difference between germ plasm and somatic plasm, the latter 

 dying, as in the Metazoa, the former capable of endless development. 

 Unlike the rhizopods, however, the germinal chromatin is retained in 

 the primary nucleus until full maturity of the cell and does not appear 

 in the cytoplasm in the form of chromidia. 



Turning after this excursion into other fields of Protozoa, to the- 



