272 WILLIAM A. KEPNER. 



characterized by having a relatively large black nucleolus which 

 lies in a vacuole (Fig. 6, B] . These are taken to be the wandering 

 cells or amoebocytes of Microstoma. 



When the nematocysts are found lying nearer the ectoderm 

 cytoplasmic strands appear extending more or less into the 

 vacuoles about the nematocysts. At P, in Fig. 6, is represented 

 what appears to be pseudopodia of a wandering cell invading a 

 vacuole. 



Whether or not in this and similar vacuoles there is evidence 

 of amoebocytes entering the vacuoles, the vacuoles in all cases 

 are filled by a cell when the nematocysts come to lie near the 

 ectoderm. About the nematocysts that have but recently reached 

 the ectoderm the cytoplasm and nucleus of the invading cell 

 are much more evident than in the cases where the nematocysts 

 have been at the surface sufficiently long or near to suffer dis- 

 charge (Figs. 7 and 8). In other words the cells seem to spend 

 their vitality in caring for these exotic nematocysts and about 

 the partially discharged nematocysts are to be found cytoplasm 

 and nuclei which indicate a depleted condition (Figs. 9 and 10). 



The nuclei of those cells do not lie at the surface of the vacuole 

 as Martin shows in his figure number four, plate 14, as he de- 

 scribes in his legend for this figure. The nucleus in each case 

 can be seen to lie well within the lumen of the original vacuole. 

 This may be determined by the study of transverse or longitu- 

 dinal sections. Figs. 7 and 8 represent two contiguous sections 

 of a nematocyst near the ectoderm. Fig. 7 was taken through 

 or near the equator of the nematocyst. Fig. 8 represents the 

 section taken immediately following that shown in Fig. 7. In 

 the eighth figure the lower surface of the section is shown. When 

 the focal plane is raised above this level three microns the nuclei 

 of the overarching mesodermal cells appear and the nucleus 

 of the invading cell disappears. Thus it is determined beyond 

 doubt that there is intimately associated with the exotic nema- 

 tocysts, when they come to lie near the ectoderm, a cell which 

 has invaded the vacuole, that had appeared about the nemato- 

 cyst within the endoderm. This cell can be seen in fresh material 

 as described earlier in this paper and in all of my permanent 

 preparations. 



