172 AETHUE E. SHIPLEY. 



size, which run into the outer end of the crown of tentacles 

 where it fuses with the dorsal ends of the lower lip, I could 

 not make out very satisfactorily whether these nerves supply 

 branches to the tentacles of this region, but I am inclined to 

 think that they do. 



A pair of very minute nerves leave the brain close to the 

 middle line ; these run to the pigmented tissue of the depres- 

 sion at the bottom of which the brain lies. At about the point 

 of the greatest circumference of each lobe the ganglion-cells 

 of the brain are in continuity with this pigmented epithelium, 

 and at one spot this epithelium is involuted into the substance 

 of the brain, its cells become enlarged and crowded with pig- 

 ment granules of dense black. The lumen of the involution is 

 practically occluded ; these pigmented involutions form the 

 eyes. 



The ganglion-cells form a cap which wraps round the fibres 

 except for about a quarter of the circumference, where they 

 come to the surface; this fibrous portion is ventral and posterior 

 in position. The whole brain is half surrounded by the large 

 blood-sinus into which the dorsal vessel opens anteriorly, and 

 which gives ofi' the vessels to the tentacles. 



The arrangement of the fibres and ganglion-cells in the 

 ventral cord is the same as that of Ph. varians (fig. 10). 



The remaining organs of Ph. Weldonii resemble those of 

 Ph. varians so closely as to render any detailed account 

 superfluous. The nephridia are two in number (figs. 4 and 7). 

 The relationship of their external and ciliated internal open- 

 ings is shown in fig. 11. The outer wall of the nephridiura is, 

 as this figure shows, continuous with the body-wall, but this is 

 for a short distance only. The organ soon becomes free, and 

 stretches back to the end of the body, and then in its most 

 extended condition may be bent back again. 



In its histological details the structure of the nephridium is 

 similar to that which I described in my former paper. The 

 inner surface is broken up into a series of crypts which are 

 lined by large glandular cells. Outside these is a meshwork 

 of muscle- fibres which I have endeavoured to depict in fig. 6, 



