2 26 BYRNES. [Vol. XVI. 



structure of the cytoplasm, and there is a complete disap- 

 pearance of any specialized central body. At this stage the 

 centrosphere corresponds to the type of the " reticulated " 

 centrosphere that Wilson has described for Toxopneustes, and 

 that Brauer has figured for Artemia. 



The series of successive stages through which the centro- 

 sphere of Limax passes seems to show that a highly special- 

 ized astrosphaere can be resolved into the reticulum of the 

 cytoplasm by a gradual relaxation, as it were, of a tension 

 exerted on the surrounding contents of the cell from a focal 

 point, the centrosome. These observations on the eggs of 

 Limax are in accordance with the view held by Van Beneden, 

 Heidenhain, Reinke, Wilson, Kostanecki, and others, that the 

 " archoplasm " has no existence as a specific substance, but is 

 only a part of the general cytoplasm. 



VI. The Centrosome. 



The study of the ova and the spermatozoa of Limax agrestis 

 throws little light on the origin and nature of the centrosome. 

 In the ovum the centrosome appears under widely different forms 

 in different stages. First, it is seen as a small deeply staining 

 point in the middle of the aster, as in PI. XI, Fig. i. In the 

 archiamphiaster stage, after a long period of growth, the central 

 body or centrosome is composed of a mass of granules (PI. XI, 

 Figs. 2 and 3). After the centrosome has divided in this stage 

 the two resulting centrosomes appear as dumb-bell-shaped rods 

 (PI. XI, Figs. 2 and 4). After the extrusion of the first 

 polar globule the centrosome again appears as a single tiny 

 granule that stains very deeply with Heidenhain's haematox- 

 ylin (PI. XI, Fig. 14). After the extrusion of the second 

 polar globule the central body apparently corresponds to the 

 granular centrosome of the archiamphiaster stage ; it reaches 

 an enormous size (PI. XII, Fig. 25), after which it becomes 

 resolved into a reticulum and finally disappears (PI. XII, Figs. 

 27 and 30). 



The centrosomes of the segmenting ^g'g appear in connec- 

 tion with the sperm-nucleus, though I have never been able to 



