118 STROPHOMENIA REGULARIS. 



become smaller, disappearing after breaking up into a small number of branches 

 that become lost among the somatic muscles. The lateral cords, on the other 

 hand, enlarge as they approach the posterior end of the pericardium where they 

 form a well-defined ganglion. From it connectives, of at least twice the diame- 

 ter of those more anterior, pass to the pedal cords. The usual commissure 

 passes dorsal to the gut; while posteriorly two or three nerves make their way 

 into the somatic musculature, and one unites with a sharply defined ganglion 

 from which branches arise whose subdivisions are distributed over the cloaca 

 and the body wall of the same region. In this species the nerves destined to the 

 dorsal sense organ are two in number. Thej' arise, widely separated from each 

 other, from the dorsal commissure, and passing along the dorsal side of the 

 animal reach the base of the sense organ. In the present specimen one of the 

 nerves for a considerable distance traverses the sinus entering the posterior end 

 of the heart. 



As is generally the case with the genus the halves of the gonad are relatively 

 wide apart in the posterior part of the body, being separated by a correspondingly 

 wide blood sinus, and more posteriorly they shade gradually into the pericardium. 

 From this latter cavity the gonoducts arise as relatively wide tubes of fairly 

 even calibre lined with cubical ciliated cells without any marked signs of glandu- 

 lar activity. At the union of the dorsal section of the gonoduct with the ventral 

 part or shell gland a number of seminal receptacles are attached, twelve being 

 present on the side of the body represented (Plate 26, fig. 8). 



As may be seen these are of varying size and are attached by short stalks 

 (Plate 24, fig. 10). In the present specimen developing ova are present incon- 

 siderable numbers, and a few are free in the cavity of the gonad; on the other 

 hand spermatozoa are of rare occurrence. However, in the dorsal section of 

 the gonoduct adjacent to the receptacles, and in the receptacles themselves 

 sperms are abundant without any definite arrangement or in some of the re- 

 ceptacles attached by their heads to the walls (Plate 24, fig. 13). Muscle fibres, 

 attached at various points to the outer walls of these reservoirs and on the other 

 hand to the body wall, pericardium or shell gland, probably cause the dilation 

 of these organs, while a delicate cuticular sheath to which the lining epithelium 

 is attached may be responsible in part for their contraction. The shell gland, 

 from side view, is somewhat irregular in outline but in cross section is very 

 synometrical (Plate 24, fig. 9). Its walls are of only moderate thickness and at 

 most levels the lumen is a narrow slit. Throughout five sixths of its extent the 

 cells, high and columnar in form, are moderately filled with a finely granular 



