332 



THE PROTOZOA 



The first division of the nucleus of the sporont has given rise to considerable 

 discussion and has been the object of much study. In the resting state the 

 sporont-nucleus is a body of relatively huge size, but the first spindle formed 

 in the sporont is, like all the subsequent mitoses, a minute structure. Some 

 authors have believed that the sporont contains two nuclei, comparable to 

 those of Infusoria namely, a very large macronucleus of purely vegetative 

 nature, which takes no part in the subsequent development ; and a minute 

 micronucleus of generative nature, from which the first and subsequent 



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FIG. 145. Stages in the formation of a generative nucleus (" micronucleus ") 

 from the primary nucleus of Pterocephalus (Nina) gracUis. A, Primary 

 nucleus showing the first appearance of the micronucleus in a clear space ; 

 B, disruption of the primary nucleus ; appearance of the micronucleus in the 

 form of a few chromosomes in the centre of a little island of nuclear substance ; 

 G, further stage in the formation of the micronucleus ; D, micronucleus com- 

 plete with the first centrosome ; the remainder of the primary nucleus in process 

 of absorption. After Leger and Duboscq (621) ; A magnified 800, B, G, D, 

 1,000, diameters. 



mitoses arise. Recent researches, however more especially those of Schnitzler 

 on Oregarina ovata, Schellack (629) on Echinomera hispida, Leger and Duboscq 

 (621) on Pterocephalus, Robinson on Kalpidorhynchus , Duke on Metamera, 

 and especially Mulsow (123) on Monocystis rostrata leave no doubt but that 

 the sporont contains a single large nucleus, which consists chiefly of vegetative 

 chromatin and other substances, but contains also the generative cliromatin, 

 relatively minute in quantity in proportion to the whole bulk of the nucleus. 



