748 PROCEEDINGS OF THE AMERICAN ACADEMY. 



its greatest width. Its length varies from 10 to 14 micra when 

 unexploded. Around the cyst is a thin layer of granular protoplasm 

 containing the flattened nucleus of the cell at the region of the greatest 

 width of the cyst. The nucleus stains deeply with basic stains, 

 the chromatin being abundant and granular. There is no trace of a 

 cnidocil or of a cytoplasmic process projecting from the free surface 

 of the cell. After staining in Mallory's phospho-tungstic acid hae- 

 matoxylin or methylen blue a thick thread may be distinguished within 

 the cyst, though not easily. It passes in a zigzag line from its attach- 

 ment for a third of the length of the cyst and fills the remaining two 

 thirds of the cyst in a tight coil (Fig. 44). When exploded the thread 

 is quite thick and short and without barbs. Nematocysts of the 

 second type (Fig. 47) are not found so abundantly. They are ovate 

 and much smaller than those of the first type. The length is 5 to 8 

 micra. The nucleus is at the broad end of the enclosing cell. The 

 thread with four or five spirals is sharply outlined even without 

 stains. Exploded, it is long and slender, without barbs. 



Sense cells (Plate 2, Figs. 8, 13, d. sns.) occur among the cover 

 cells, but are readily found only in the nematocyst batteries, where 

 their bristle tips can be seen in favorable sections and where their 

 nuclei reveal them by the size, which is smaller than that of the cover- 

 cell nucleus. The sense cell is narrow and spindle-shaped with a 

 long process extending into the mesogloea. Its protoplasm is slightly 

 more evenly granular than that of the cover cells, though not greatly 

 different from it; but its nucleus is small and round and can be readily 

 distinguished from the larger nucleus of the cover cells. The bristle 

 point is exposed between the cover cells, or between these and the 

 nematocyst cells. 



The subepithelial part of the ectoderm is made up of interstitial 

 cells, globular cells with granules, nematocyst cells, and ganglion 

 cells. It is not a sharply defined layer, since the cover cells and the 

 sense-cell processes pass through it. The interstitial cells (Plate 2, 

 Figs. 18, 20, cl. in.) are globular or have a central body with branching 

 processes. In fact, the cells, or some of them, may change their 

 shape in an amoeboid manner. The cytoplasm is similar to that of 

 the cover cells; the nucleus may be smaller, though it varies greatly 

 in size. The granular cells are filled with comparatively large granules 

 and stain sharply with eosin. They have the appearance of the 

 granular cells found in the mesogloea of the coenenchyma. Besides 

 cells containing fully formed nematocysts, there are some which show 

 stages in the formation of the nematocysts (Fig. 18, cl. nmcys.). 



