86 bulletin: museum of comparative zoology. 



The classes (a), (c), and (d) are similar in that they all contain chro- 

 matin, but differ in the manner in which this chromatin is arranged. 

 Of these three classes the last (d) is the one which most resembles 

 the karyosphere as observed by myself in Scolopendra heros. This 

 structure in Lithobius is in all respects like a miniature nucleus. It 

 contains all of the chromatin of the cell in the form of granules depos- 

 ited upon a reticulum of limn fibres, and is surrounded by a definite 

 membrane. This membrane I have never been able to demonstrate in 

 Scolopendra, and indeed I do not believe that it exists there, although 

 it may well be present in Lithobius. The nucleolus gives rise in the 

 first maturation division to the chromatin thread, from which the chro- 

 mosomes are derived. After the completion of the first division it is 

 said to be again reformed. On the reconstruction of the daughter nuclei 

 (p. 301), " On peut en eftet y distinguer deux etapes ; (a) la formation 

 du nucleole, (b) la formation du noyau proprement dit. La nucleole se 

 reconstitue le premier, et a la facon d'un noyau oi'dinaire." From my 

 own observations upon Scolopendra and more superficial study of Geo- 

 philus, Scutigera, and Lithobius, I am convinced that no such process 

 ever occurs. Carnov's Figures 210 and 216, which he has interpreted 

 as the telophase of the first maturation division, are indeed drawings of 

 cells in the vesicle stage. Carnoy also observed this " nucleole noyau " 

 in two other genera of Chilopoda, Scutigera and Geophilus, where in 

 structure and behavior it is very similar to that in Lithobius. But in 

 Scolopendra dalmatica the " nucleolus " is found to belong to an entirely 

 different class. Concerning this body he speaks as follows (p. 302): 

 '■' Le boyau y est uniformement distribue, et le nucleole . . . n'est pas 

 un nucleole-noyau, mais un nucleole plasmatique. Sa constitution est 

 done celle d'un noyau ordinaire." Later he says : " Le debut de la 

 caryocinese s'annonce par plusieurs phenomenes concomitants: la scis- 

 sion du boyau, la fusion du nucleole, l'apparition des premiers rudiments 

 du fuseau et enfin la naissance des asters." Then, after describing the 

 formation of the chromosomes, he adds : "En meme temps que le boyau 

 se segmente, le nucleole se liquefie pour enrichir le caryoplasma ; e'est 

 en vain que nous l'avons recherche dans les phases subsequentes." 



Thus the facts of the case in S. dalmatica seem to be these. One of 

 the first phenomena of mitosis is the disintegration of the nucleolus. 

 This is accompanied by the formation of the chromosomes. Later, 

 when the chromosomes are completely formed, the " nucleolus " is no 

 longer to be seen. These observations as far as they go entirely agree 

 with mine on S. heros, and it seems possible that further study might 



