NUCLEOLAR STRUCTURES OF THE CELL. 169 



many spermatocytes and of some germinal vesicles (particu- 

 larly of polychaete annelids), which are less frequent in somatic 

 cells. These double nucleoli are usually formed of two apposed 

 spheres, of which the one is a true nucleolus, while the other 

 consists of a substance staining like chromatin. Not only may 

 these bodies occur in pairs, but in chains of three or more (as 

 first noted by Hermann in follicle cells of the testicle of the 

 mouse) ; in other cases the true nucleolus may be separated 

 from the other sphere, or the two may be at one time sepa- 

 rated and at another united. Many of the older observers, 

 who did not make use of sections, have described as double 

 nucleoli, true nucleoli which enclose a large excentric vacuole, 

 considering this vacuole to be a second nucleolus applied to the 

 first ; such cases should not be regarded as double nucleoli. 

 These remarkable " nucleolar " structures, which stain like 

 chromatin, have been observed by numerous writers, but as 

 yet no satisfactory description has been given of their mode of 

 origin. They have been observed by me in spermatocytes of 

 various insects, in hypodermal and other cells of Carpocapsa, 

 and in follicle cells of the testicles of Plethodon and Mus. 

 Whether structures comparable to them occur in germinal vesi- 

 cles, I have not as yet been able to determine. In two cases I 

 have followed their mode of formation, and these cases may be 

 described here. 



One point may be emphasized : the term " chromatin nucle- 

 olus " should be applied only to those structures which can be 

 proved to be derived from chromatin ; in those cases where 

 their mode of formation has not been followed it seems best to 

 avoid the use of a special term, since it is by no means certain 

 that all these structures should be classed in the same category. 



i. The Spermatocytes of Eiichistus (Pentatomd}. The sper- 

 matogonia contain only a true nucleolus, which disappears in 

 the prophase of mitosis. The fourteen chromosomes of the 

 last spermatogonic division are halved in metakinesis, so that 

 each daughter-cell (first spermatocyte) receives fourteen daugh- 

 ter-chromosomes. The stain necessary for demonstrating the 

 consequent phenomena is one which will stain the dividing 

 chromatin a different color from the resting chromatin : the 



