NUCLEOLI IN EUSCHISTUS VARIOLARIUS. 223 



In Euschistus we have not been able to demonstrate its pres- 

 ence at any stage of the growth-period of the spermatocytes. In 

 sections we often find faintly staining areas that might be inter- 

 preted as an achromatic nucleolus, but in view of the possibility 

 of artefacts in such preparations, we hesitate to interpret them as 

 true nucleoli, unless we can support the interpretation in our 

 smear preparations. Until this point can be settled we are not 

 justified in drawing any conclusions from the obvious differ- 

 ence in type between the nucleoli in the male and female cells of 

 Euschistus, though we have here quite as marked a sexual dif- 

 ference of the nucleoli, as any that has been shown for the 

 chromosomes, a difference that appears in no way associated with 

 the maturation divisions of either germ cell. 



In comparing the achromatic nucleolus of the oocytes of 

 Ensc/iishis with the principal nucleolus of AllolobopJwra we find 

 some individual differences between the two. The principal 

 nucleolus of Allolobophora is clearly differentiated in the young 

 oocytes as a small, dense chromatic body, and it can be traced 

 uninterruptedly through the entire growth period of the oocytes. 

 During this period it increases in size, proportionately to the 

 growth of the nucleus, gradually becomes less dense and less 

 chromatic, and finally, when the germinal vesicle has reached its 

 maximum size the principal nucleolus often appears as in Photo 

 31. In some cases, however, its dense and chromatic character, 

 distinctive of the earlier stages, persists until the chromosomes are 

 fully formed or again it may so completely disintegrate that only 

 a clear space remains as evidence of its existence. 1 



The achromatic nucleolus of Euschistus differs from the prin- 

 cipal nucleolus of Alloloboplwra in not being present in the young 

 oocytes as a small dense chromatic nucleolus. We have been 

 unable to demonstrate any such chromatic body in the young 

 oocytes of Euschistus. In the youngest stages in which a nucle- 

 olus is found, it appears as clearly achromatic as when it has 

 reached its maximum growth in the germinal vesicle compare 

 Photos 13 and 16 with Photos 18 to 30. There are also indica- 

 tions that it is often not formed until after the oocytes have attained 

 a definite growth, for in such clear preparations as are shown in 



1 Foot and Strobell ('05), Photo 122. 



