276 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



contribution of Boveri (:0l) in which he discusses the centrosome and 

 (p. 125) defines it as follows : " Ein Korper, an den die Spharenradien 

 direkt herantreten, ist das Centrosoma." The body which occurs at 

 the centre of the "spheres attractives" is named by Van Beneden et 

 JS^eyt ('87) the " corpuscule central;" it is this which, according to the 

 definition of Boveri, is to be interpreted as the centrosome. The centro- 

 some may become differentiated into two distinct regions, the centriole 

 in the centre, and the centroplasm surrounding it. The latter is defined 

 by Boveri (:01, p. 32) as follows : " Was nun die feinere Zusammen- 

 setzung dieses Ceutralkorperchens anlaugt, so lasst sich in seiner 

 Substanz, die ich fortan als Centroplasma bezeichnen will, bei keiner 

 Untersuchungsweise eine Spur einer radiaren Struktur erkennen." I 

 have decided to use in my description of the centrosome Boveri's terms 

 and definitions of centroplasm and centriole. 



As long as the egg of Haminea remains in the ovotestis, the mitotic 

 figure which replaces the germinative vesicle occupies a central position, 

 and the deutoplasm constitutes a layer of practically uniform thickness 

 at the periphery of the egg, the cytoplasm — free from yolk except for 

 a few isolated spheres — being largely concentrated in the region 

 immediately surrounding the mitotic figure. This condition is well 

 illustrated in Figure 16 (Plate 3). It is at first impossible to say which 

 pole of the spindle will eventually reach the surface of the egg ; but as 

 soon as the egg is laid, the whole mitotic figure and the immediately 

 surrounding cytoplasm move peripherally. The yolk thus comes to 

 predominate in one portion of the egg, which we may now designate as 

 the nutritive part. Figure 19 (Plate 4) shows the mitotic figure migrat- 

 ing into a radial position. At tliis stage the yolk granules have 

 disappeared between the outer pole of the spindle and the periphery of 

 the egg. The cytoplasm accumulated here continues to occupy this 

 region of the egg, which we may now designate as the formative part. 



Centrosome. Figures 68 (Plate 10) and 19 (Plate 4) are from 

 eggs fixed immediately after deposition. The centrosome, as compared 

 with the conditions in an egg from the ovotestis, has increased in 

 size ; the centriole, though a single body, is irregular in outline ; the 

 centroplasm (Figure 21, c'pL), the region immediately surrounding 

 the centriole (c7.), is distinct, and, like the centriole, slightly irregular in 

 outline ; it takes a very deep plasma stain, which in the early stages 

 often makes difficult the task of distinguishing it from the centriole, 

 especially if the latter has been overstained. 



Figures 20--23 (Plate 4) show a series of progressive changes in the 



