42 PEOTOZOA [CH. 



not worn out in the same manner, is received. The micronucleus 

 and meganucleus are sisters and the micronucleus corresponds to the 

 "chromidium" of the Rhizopoda which is given off from the primary 

 nucleus and which gives rise to the gametes. The fact that it divides 

 into eight pieces of which only one survives probably points back 

 to an ancestral condition in which numerous gametes were found. 

 Vvrticella conjugates in a similar manner to Paramecium, but one 

 of the conjugants is a small motile person, the other a large ordinary 

 fixed one. The small partner never frees himself and after delivering 

 the male gamete and receiving another male gamete from the larger 

 partner, he degenerates and is absorbed as food by the larger fixed 

 one so that in every conjugation one individual disappears. 



Opalina. found in the intestine of the Frog, is a most aberrant 

 Ciliate and stands in remote relationship 

 to the rest ; it is holotrichous like Para- 

 mecium. This animal is 'thin and plate- 

 like. Opalina is further remarkable for 

 possessing a large number of nuclei (1, 

 Fig. 14), which is a rare occurrence 

 amongst the Ciliata. When, however, 

 division commences it continues until the 

 resulting pieces have only one nucleus 

 each ; they then grow and do not divide 

 again till they acquire the size they had 

 FIG. 14. Opalina ranarum. before division took place and also the 

 Highly magnified. same number of nuclei. Hence we might 



From Bronn. regard the multiplication of the nuclei as 



1. Nuclei. 2. Ectoplasm. the real re p ro duction of this form, the 

 division of the protoplasmic body being 



of lesser importance and setting in later. When the Frog lays its 



eggs in spring the nuclei of the adult Opalina discharge chromatin 



granules into the protoplasm forming chromidia which aggregate as 



small dense secondary nuclei; the original nuclei remain as pale spheres 



for some considerable time. This ejection of chromidia corresponds 



to the breaking up of the micronucleus in other Ciliata. Division 



then takes place until the daughters have only four nuclei each. They 



then encyst themselves, the cysts are discharged into the water and 



if swallowed by a tadpole burst, giving vent to four ciliated gametes 



each with one nucleus, which then conjugate with one another. 



Passing from the Ciliata, we next come to a small group called the 



S u c tor i a, which are allied to the Ciliata, for their buds 



commence life as small ciliated forms. When they 



