372 PROCEEDINGS OF THE ACADEMY OF [May, 



A much smaller space is occupied by the much smaller germ cells, 

 placed near the duct, characterized by very small, deep-staining nuclei 

 and clear cytoplasm. Gast correctly noted these two kinds of cells 

 and their differences. The egg cells do not reach their full size within 

 the germarium, but only when they leave it and reach the oviduct, 

 which becomes dilated by them to serve as a uterus for the complete 

 embryonal development ; as many as five large embryos are found in 

 the uterus at one time, representing different stages of development. 



N'ervous system. — Stokes was the only one to see this organ complex 

 before the time of the very thorough account by Gast. The cerebral 

 ganghon lies in the mid-line above the alimentary tract (PL XVIII, 

 Cer., figs. 1, 2), at the junction of corona and trunk or a little anterior 

 to this point. Seen from the side (fig. 2) it appears ovoid, a little 

 longer than high. Seen from above (Cer., figs. 1, 6) it is found to be 

 widest in the transverse plane. Through each side of it passes a visceral 

 longitudinal muscle (levator coronse. I.e.). In life as weh as in stained 

 preparations the following nerves can be seen passing from this cerebral 

 ganglion (figs. 1, 6). From its dorso-anterior edge three pairs of deli- 

 cate nerves, which converge to the dorsal sense-organ (D.Sens.O.), 

 i.e., pass upward and forward from the ganglion. Each of these nerves 

 has a nucleus at the point where it joins the ganglion. From each side 

 pass out at least eight nerves : one for the latero-anterior sense-organ 

 (A.Sens.O); one for the latero-posterior sense-organ (L.Seyis.O.); two 

 large nerves which pass back from the latero-posterior angle of the 

 ganglion but which could be traced only a short distance ; and four 

 other nerves which could be traced only a short distance, but one or 

 two of which appeared to be connected with the nephridial tubules. 

 The ganghon and its nerves are thus strictly bilaterally sj-mmetrical. 



Now the three pairs of nerves which can be traced to the three sets 

 of sense-organs all arise from the dorsal margins of the ganghon; the 

 dorsal portion of the ganglion may then be essentially sensory. The 

 two large ventral posterior nerve pairs arise from two large cells, each 

 evidently bipolar, placed at the ventro-posterior margin of the gang- 

 lion; Gast noted only one of these and only one posterior nerve. These 

 two cells are characterized by their great size (they might be called on 

 this account neurochord cells, with reference to similar huge cells in 

 Nemertini, Annelida and Crustacea), and the large size of their nuclei. 

 Since these differ so markedly from the demonstrated sensory nerves, 

 it is very probable that they innervate either the musculature or the 

 viscera, i.e., that they are either motor or splanchnic in function. 

 Then since their roots are ventral in the ganglion, it would follow that 



