i6o 



MANUAL OF ELEMENTARY ZOOLOGY 



history with that of Paramecium suggests (l) that the destruction of 

 the old nuclei corresponds to that of the meganucleus of Paramecium, 

 (2) that the divisions of the micronuclei of the latter before conjugation 

 may perhaps be the remains of a lost habit of forming a number of 

 gametes like these of Opalina. 



It does not appear that any of these animals is harmful to the frog. 



Attention may now be called to certain facts of the behaviour of pro- 

 Rl f tozoan nuclei which, doubtful of interpretation though 



Protozoan" tne y ' De ' are none tne ^ ess suggestive. Protozoa often 

 Gametes. (perhaps always) lose a portion of their nucleoplasm 



before conjugation. This may take place by mitosis, and 

 in such cases a definite halving by the loss of chromosomes has some- 



FlG. 100. ■ 



ranarum. 



A, Ordinary individual in longitudinal fission; B, the same in transverse fission; 

 C, small encysted individual (distributive phase) ; D, gamete ; E, encysted 

 zygote. 



times been established (as in the micronucleus of Paramecium, p. 135). 

 No doubt the function of such a process is the same as that of the ripen- 

 ing of the gametes of higher animals (p. 106). In other cases {Entamoeba, 

 p. 145) there is merely a non-mitotic throwing out from the nucleus of 

 chromatic matter, and this is perhaps comparable not to the " reduction 

 division " of Paramecium and the higher animals, but to the destruction 

 of the body nucleus (meganucleus) of Paramecium at conjugation, and 

 this, more distantly, to the parting of body and germ in the Metazoa. 

 It seems that in Opalina both "reduction" and the loss of body 

 chromatin take place. Once more in these facts is probably to be seen 

 the analogy of the protozoon with the whole body of a metazoon, rather 

 than with one of its cells. 



