500 PROCEEDINGS OF THE AMERICAN ACADEMY. 



masses of achromatic material, this all being incorporated in the nu- 

 cleoli, of which there are several, the amount of nucleolar material 

 being greater. Usually each nucleolus contains one or more chromo- 

 somes and thus constitutes a karyosphere (Figures 14-17). The num- 

 ber of karyospheres in a nucleus varies from one (Figure 15) to four 

 (Figure 18) or even six, the most common number being two (Figure 

 16), while three are often seen (Figures 14, 17). When the number 

 of karyospheres is greater, the relative amount of chromatin in each is 

 smaller and the chromatin occurs in more definite masses. Often it 

 is arranged in the form of a single thread embedded in the nucleolar 

 material (Figure 14), while in other cases it occurs in several irregular 

 masses (Figures 14, 1.5, 17). It is usually enveloped in the nucleolus 

 and not deposited upon the periphery, as in Lithobius multidentatus. 



The origin and behavior of the chromosomes during the prophase 

 of the first spermatocyte of myriapods has been described differently 

 by different workers. The first account is that by Carnoy (85), 

 which deals with the spermatocyte mitoses of Lithobius forficatus, 

 Scutigera arachnoides, Geophilus, and Scolopendra dalmatica. In 

 Lithobius, Scutigera, and Geophilus the nucleole-noyau (karyosphere) 

 gives rise to the chromatin thread, from which the chromosomes are 

 derived. The process of tetrad formation was not studied at all. In 

 Scolopendra dalmatica the nucleolus is said to take no part whatever 

 in the origin of the chromosomes. 



Later investigators upon European myriapods have arrived at re- 

 sults quite different from those of Carnoy. Meves und von Korfif 

 (:0l) confined their observations almost entirely to the peculiar modi- 

 fication in the achromatic division figure of the first spermatocyte of 

 Lithobius forficatus. The chromosomes were but little studied, and 

 those figured are already in the form of distinct elements. The de- 

 scription, however, gives the impression that they arise from the net- 

 work of the nucleus. 



In several short papers from the University of Nancy, P. Bouin, M. 

 Bouin, and R. Collin have dealt briefly with the chromosomes, al- 

 though most of their work has been upon achromatic structures. In 

 Geophilus linearis P. Bouin et B. Collin (:0l, page 101) find no con- 

 nection between the large " nucleolus " and the origin of the chromo- 

 somes, but on the contrary state that these elements arise from a 

 chromatic reticulum: "Le reticulum chromatique est constitud par 

 de tres fins microsomes distribuds sur les mailles du rdseau de liuine ; 

 au niveau des points d'entrecroisement de ce r^seau, ils sont rassembl^s 

 en amas plus ou moins volumineux. Ces microsomes chromatiques 

 se r^unissent bientot en petites masses qui se condensent rapidement 



