6 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



spheroidal bodies. In Figure 14 the compartments contains spermato- 

 cytes of the first order ; c, spermatocytes of the second order and sperma- 

 tids just after the last division. (Compare Fig. 23 and Explanation of 

 Figures.) The cells of b each contain one or two bodies which I con- 

 sider nucleoli, since they react to the stains quite differently from the 

 chromosomes. Figures 53-59 (Plate II.) represent cells quite commonly 

 met witli among the spermatocytes ; they are numbered in the order in 

 which I think they succeed one another. In a single compartment may 

 be found spermatocytes in several diflFerent conditions ; the earliest 

 seems to be that in which the nucleolus lies in the centre of the nucleus 

 with the chromatic spherules arranged radially about it (Fig. 53). The 

 nucleolus then moves to the periphery of the nucleus, and appears mean- 

 time to have divided into two portions (Figs. 55, 56), one of which 

 passes into the cytoplasm, while the other remains in the nucleus (Figs. 

 58, 59) ; later, both parts appear outside the nucleus and on diametri- 

 cally opposite sides of it. 



Hertwig ('90) has noticed the disappearance of the nucleoli in the 

 spermatocytes of Ascaris megalocephala just before the appearance of the 

 centrosomes. Brauer ('93) figures the centrosomes as arising singly in 

 each nucleus and dividing either inside (uuivalens) or outside (bivalens) 

 the nucleus, according to the type. But Brauer saw nucleoli in the 

 same nucleus with the centrosomes and differing from them in stain- 

 ability. Born ('94) maintains that the nucleoli have nothing to do with 

 either reproduction or cell division. He says : " Die Nucleolen stehen 

 in Beziehung zum individuellen ZelUeben, nicht zur Fortpflanzung, denn 

 beim Beginn der Mitose verschwinden sie um nach Beendigung der- 

 selben — im Ruhezustand des Kerns — wieder aufzutreten." 



Thus the nucleoli have been supposed to give rise to the centrosomes, 

 to be modified chromatin, — a stage in the evolution of a cliromosome, — 

 to be excretory organs of the nucleus (Hacker, '93), or to serve some 

 unknown function in the economy of the cell (Born, '94). The nucleoli 

 are found by Born to be very numerous and large in the germinative 

 vesicle of the egg of Triton during the time when the chromatin is 

 inconspicuous ; but they disappear entirely before the formation of the 

 first polar globule. 



Since there is such disagreement about the origin, function, and 

 fate of the nucleoli, it is probable that different structui'es have been 

 called nucleoli by different authors. The several bodies in Cicada seen 

 in and near the nucleus in Figures 50 and 53-61 (Plate II.) — in 

 Figures 53, 54, as a single body, in Figures 55, 56, as two bodies, in 



