22O KATHARINE FOOT AND E. C. STROBELL. 



intensely as the chromosomes, and in both forms we sometimes 

 find one and sometimes two chromatin nucleoli. 1 The comparison 

 may be carried even a step further. We may compare the 

 chromatin nucleolus of Alloloboplwra to the chromatin nucleolus 

 of some forms where it is figured at one pole of the first spindle 

 as an undivided chromosome. The chromatin nucleolus of 

 Allolobophora often persists through the first division, and in such 

 cases it is either free in the cytoplasm, near the spindle, or at one 

 pole of the spindle in which position it strongly resembles the 

 undivided chromosome figured in so many forms. Photo 32 

 shows a section through the first maturation spindle of an egg of 

 Allolobophora, and a comparison of the chromatin nucleolus at 

 the upper pole of this spindle, with the chromatin nucleolus in 

 the germinal vesicle of Photo 31 leaves no doubt of the identity 

 of the two structures. The identification is further confirmed by 

 the clear demonstration in this and the adjoining sections of all 

 eleven chromosomes in the equatorial plate of the spindle. If the 

 chromosomes of Allolobophora were spherical as they appear in 

 sections of so many forms, we could not so easily identify the 

 chromatin nucleolus, for it stains exactly like the chromosomes. 

 Such a case is described by Arnold ('08) in the spermatogenesis 

 of the Coleopteran Hydrophilus piceus. During the rest stage 

 the chromatin nucleolus of this form is easily recognized, but he 

 finds it impossible to differentiate it from the chromosomes during 

 the first prophase, because the chromosomes at this stage are 

 also spherical and both structures stain alike. He is able to 

 identify it again at the first metaphase, where it lies in the cyto- 

 plasm near the spindle, or within the spindle at one pole. It 

 persists through the first division, but disappears before the 

 second mitosis. 2 It is clear that in its origin, behavior and time 

 of disappearance the chromatin nucleolus of the spermatocytes of 

 HydropJiilits closely resembles the chromatin nucleolus of Allo- 

 lobophora, with the exception that the latter does not invariably 

 persist through the first division. Arnold ('oS) supports Moore 

 and Robinson's ('05) conclusion that the chromatin nucleolus of 



1 Foot and Strobell ('05), Photo 115. 



2 Wheeler ('97) figured the nucleolus of the germinal vesicle of Mysostoma 

 glabrum persisting through the second cleavage and he says that in some cases it 

 persists through the next stage, and perhaps even later, page 35. 



