402 MONTGOMERY. [Vol. XIII. 



do not correspond to the number or position of the lateral 

 nerves (" spinal " nerves) of the lateral chords. It would be 

 important to determine whether the sequence of such zones 

 corresponds, for instance, to the metamerism of the gonads; 

 since my specimen was immature with undeveloped gonads, I 

 could not determine this point. If such a regular metamerism 

 of the areas could be proved, then the lateral chords of the 

 nemerteans — in which no segmental localization of ganglion 

 cells producing ganglia has as yet been shown — could be con- 

 sidered as in the inceptive stage of producing such ganglionic 

 localizations. Unfortunately, however, the determination of 

 this point, which has a certain phylogenetic importance, would 

 necessitate the preparation of many thousand sections, since 

 the adult worm should furnish the basis for such a study. But 

 it might more easily be investigated on smaller species of the 

 genus. 



b. Structure. — The structure of the giant ganglion cells IV 

 of Cerebratuhis (Figs. 27-29, 32) has much resemblance to that 

 of cells III of the same species, though there are certain 

 differences which may usually serve to distinguish them. 



The nucleus (Fig. 31 a-e) may be nearly spherical, but is 

 more frequently spherico-oval. It usually has a proximal posi- 

 tion within the cell, close to the cell membrane, is seldom 

 central, and never distal in position. In it small masses or 

 granules of chromatin {Chr) of adequal size are arranged 

 peripherally on the inner surface of the well-marked nuclear 

 membrane; and these do not form a continuous layer, as is 

 frequently the case in the nucleus of III, but are placed at 

 more or less regular distances apart. The central portion of 

 the nucleus, which Burger ('90b, cf. my remarks on the nucleus 

 of III) has erroneously supposed to be filled with a " Blaschen," 

 is mainly filled with the nuclear sap; this sap, in contrast to 

 that of the other ganglion cells, stains faintly with haematoxylin. 

 In it vestiges of a finely granular, achromatic reticulum (mesh- 

 work .'') may be observed (Achr.). A thin mass of chromatin 

 envelops the nucleolus {n). The latter is never absent, is of 

 large size, and almost always peripherally situated; it has thus 

 the same position in the nucleus as the latter has in the cell. 



