616 GEORGE T. HARGITT 



cells usually are. Consequently one may say that in the many 

 medusae examined there was no evidence of a migration through 

 the entoderm tissue of the radial canals, and no evidence of inter- 

 stitial cells or primordial germ cells in the tissues of the canals 

 or tentacle bulbs. 



The only possibility remaining is whether germ cells may 

 pass through the cavity of the canals to the tentacle and thus 

 to the budding medusae. Such a course is improbable since a 

 passage entirely through the supporting layer and entoderm 

 would be necessary before the germ cells could enter the gastro- 

 vascular cavity. It is also probable that germ cells in the gas- 

 tro vascular cavity would be subject to digestive action of en- 

 zymes and could hardly escape some disintegration as a result. 

 Of all the medusae examined the only cases found where solid 

 matter was present in the canals are illustrated in figures 43 

 and 44. The rarity of this condition is probably indicative of 

 its unusualness, but these inclusions will bear careful scrutiny. 

 Figure 43 is a longitudinal section of the aboral portion of a 

 radial canal near the point where it joins the large marginal 

 bulb. The substance within the canal extended over several 

 sections but there was not, in either mass, any sign of a nucleus; 

 there were a few deeply staining spots which might have been 

 of nuclear origin, but these were small and scattered. The 

 cytoplasm was much vacuolated and filled with large and small 

 spherules of different composition or density, and the edges of 

 the masses were irregular and broken. Such masses resemble, 

 somewhat, the tips of cells like those shown in figure 41, and do 

 not look like germ cells. But whether they might be considered 

 as germ cells is of no significance since their condition shows 

 clearly that a disintegration is taking place. They could not, 

 therefore, be active and functional cells. 



Figure 44 gives us a different picture. This is a section of a 

 radial canal near its union with the stomach. The entoderm 

 cells of the canal are like those in figures 42 and 43 and there is 

 no difference in the ectoderm and jelly. The cell which is 

 within the canal does resemble a germ cell in some ways in that 

 there is a deeply staining, finely granular and compact proto- 



