EAND : NERVOUS SYSTEM OF LrMBRICID^. 91 



SchafFer ('96) described centrosomes in certain cartilage cells of 

 Myxine glutinosa and also in nerve cells of the cranial ganglia of Petro- 

 myzon planeri 15.5 cm. long. His material was fixed in picro-subliraate 

 and stained in haemalum-eosin. SchafFer found cells with the nuclei 

 excentric. The cytoplasm was very finely granular, and in it was com- 

 monly found a structure forming " eine Art von Gegengewicht im Proto- 

 plasma gegeniiber dem Kern " (p. 26). These cytoplasmic structures 

 appeared in some cases as merely small areas of irregular shape and 

 varying size, staining red in contrast to the surrounding blue. Often 

 two such areas of unlike form and size lay near together. In some 

 cases a small clear space surrounded the darker area. In still other 

 cells a circular clear area contained a small central granule, and at one 

 side of the clear area lay an irregularly shaped red-staining mass similar 

 to those found where no clear area and granule were present. Schaffer 

 interprets the granule, clear area, and red-staining mass as centrosome, 

 sphere, and archoplasm, respectively. He attributes the failure to find 

 all three of the structures in so many cells to unfavorable planes of cut- 

 ting, or to other causes. Xo radial arrangement of the cytoplasm was 

 seen. He suggests that the structures described may be concerned 

 in nuclear divisions of the ganglion cells, since he has often seen in 

 Petromyzon ganglion cells with two nuclei. 



McClure ('96, '97) described centrosomes and spheres in the nerve 

 cells of Helix and thinks they may exist in Limulus. In Astacus, Cam- 

 barns, Homarus, Lumbricus, Arion, and Limax he failed to find these 

 structures. In unipolar ganglion cells of Helix with a transverse diam- 

 eter between 17 fi and 22 fi he finds excentric nuclei often flattened, 

 or more frequently kidney-shaped. His figures show the nuclei lying 

 at the end of the cell opposite the nerve process, and the flattened or 

 concave side of the nucleus is never "directed exactly opposite to the 

 base of the axis-cylinder process, but always to a point on one side of 

 it," "In the body of the cell, directly opposite the invagination [of the 

 nucleus], a disc-shaped structure was found.'' The disc is finely granu- 

 lar, but shows no radial aiTangement. " Within these discs and at 

 about their centre, two or three small granular bodies were present 

 which stained much deeper than the surrounding granules and which 

 I have taken for centrosomes." A zone of cytoplasm immediately 

 surrounding the disc stains darker than the disc, because of a concen- 

 tration of small chroraophilous granules, but no radial arrangement 

 among these granules is to be seen. The centrosome and sphere were 

 best seen in material fixed in Flemminofs fluid and stained in iron- 



