NUCLEOLI IN EUSCHISTUS VARIOLARIUS. 221 



the first spermatocyte is not a chromosome and does not take 

 part in either division. His evidence for this is very convincing, 

 he says, if it is to be interpreted as an accessory chromosome 

 which remains undivided in the first spindle it should divide in 

 the second spindle, and half the second spindles should show one 

 more chromosome than the other half. Arnold finds, on the 

 contrary that the number of chromosomes in the second spindle 

 is as constant as the number in the first. He gives in the follow- 

 ing table the results he obtained : 

 Out of 100 counts of first meiotic : 



85 per cent, gave 15 gemini and the nucleolus. 



ij it over T C " " " " 



8 " " " under 15 

 Out of another 100 counts of first meiotic : 



90 per cent, gave 15 gemini and the nucleolus. 



3 " " " over 15 " " " " 



7 " " " under 15 " " " 



Out of 100 counts of second meiotic : 



91 per cent, gave 15 chromosomes. 



6 " " " over 15 " 



3 " " " under 1 5 " 



The resemblance between the chromatin nucleolus of the first 

 spermatocyte of insects and the chromatin nucleolus in the ger- 

 minal vesicles of some forms has been noted by Hacker ('07) who 

 says, that in those cases in which the heterochromosome is fig- 

 ured as a cap-shaped mass on a large pale plasmosome, the two 

 structures are extraordinarily like the two kinds of nucleoli in 

 the germinal vesicles of the lamellibranch type. He says : " So 

 kann man sich dem Eindruck nicht entziehen, das z. B. das, 

 ' akzessorische Chromosom ' in den ruhenden Spermatocyten 

 von Scolopendra (Blackman, 1905, tab. 2, fig. 10-15) fruherein- 

 fach als ' Nucleolus ' beschrieben worden ware, und man ist gen- 

 eigt, sich zu fragen, ob denn in alien vorliegenden Angaben 

 bereits eine reinliche Scheidung zwischen den Heterochromoso- 

 men und den echten Nucleolen (Plasmosomen) durchgefiihrt ist. 

 Es sei mirauch gestattet, darauf hinzuweisen, das die von Wilson 

 u. a. gegebenen Bilder, in welchen ein Heterochromosom als 



