1904.] NATURAL SCIENCES OF PHILADELPHIA, 375 



terior end of the enteric cavity with the ectoderm, and this latter point 

 of contact is just below the large excretory cell. Fig. 88 shows a sec- 

 tion through this region, showing the excretory cell to be much vacuo- 

 lated and to lie for the most part below the ectoderm. At a consider- 

 ably later stage (figs. 109, 110) its position and structure are shown 

 just before the vehger escapes from the egg capsule. A large nucleus, 

 which usually contains several small nucleoli and having the general 

 appearance of nuclei in cells which have for a long time remained 

 undivided, lies at the lower end of the cell. The cytoplasm is greatly 

 vacuolated and at its peripheral end, where it meets the exterior, is 

 seen a deep pit with constricted mouth. This appears to function 

 as an intra-cellular duct, for it comes into connection at its inner end 

 with the large vacuoles which fill the cell. Just above and anterior 

 to the large cell is a group of smaller ones which contain darkly stained 

 nuclei and pigment granules. One of these, the largest, also contains 

 vacuoles and lies nearest the cell 3c"". In somewhat older larvse one 

 or two of these smaller cells, which lie close to 3c"", have increased 

 much in size, JDecome greatly vacuolated and appear to function as 

 their larger neighboring cell. These smaller accessory excretory cells 

 are also doubtless of ectodermal origin and, since they lie between the 

 principal one and the blastopore, are doubtless derived from the same 



quartet. 



In- addition to the excretory cells above described others of a similar 

 nature are found in the larva of Fiona. Sections (figs. 90, 91) of fairly 

 well-developed veligers show^ two cells (Nph) nearly symmetrically 

 placed on the two sides of the body just behind the constriction sepa- 

 rating head from body region. These cells contain large nuclei and 

 their protoplasm is clear and greatly vacuolated. In a shghtly older 

 stage (the oldest larva examined) yellowish-brown granules are very 

 evident, lying in the meshwork of the vacuolated cytoplasm. The 

 cell on the left side (fig. 91) lies just to the side of and slightly higher 

 than the otocyst of that side, being closely associated with its ganglia, 

 while the one on the right side (fig. 90) lies higher and is in close prox- 

 imity to the smallest cells of the large excretory organ of that side. It 

 may be distinguished from the cells of this organ by its clear cytoplasm 

 and the color of the granules lying in it. In later stages another cell 

 of similar nature may be seen beside the one on the right side, but 

 only one has been observed on the left. The origin of these cells is not 

 known. In earlier stages cells of shghtly smaller size lie in the regions 

 which they later occupy, but cannot be distinguished in structure 

 from neighboring mesodermal elements. However they lie close to 



