766 CITARLER L. r.OULENflER. 



(ft) The neraatocjsts found in the endoderm are always 

 undischarged. 



(h) Favourable sections show them to be accompanied by 

 their nematoblasts. 



(r) The nematocysts are never to be found near the free 

 margins of the endoderm cells, but, for the most part, 

 between the more basal portions of these cells near the 

 structureless lamella. 



These thread-cells can, obviously, not become functional in 

 this position, and the only possible explanation of their 

 occurreuce here is that they are making their wa}' from their 

 place of origin to some battery where they can be of use. 



At this point it may be avcII to review the distribution of 

 stinging-cells in the ectoderm of the manubrium. The chief 

 battery is situated around the mouth-opening; here the 

 thickened ectoderm forms a circular lip crowded with nemato- 

 cysts, and constitutes a powerful organ of offence (PI. 42, 

 figs. 3 and 4). The ectoderm of the remainder of the manu- 

 brium proper consists of a single layer of low, closely fitting 

 epithelial cells with occasional isolated nematocysts ; it is to 

 be noticed that here, as well as on the oral lip, interstitial 

 cells are completely absent. At the base of the manubrium 

 is the broad stomach, the ectoderm of which is considerably 

 thickened and forms the conspicuous gonad. 



Interstitial cells and developing thread-cells being absent 

 from the more distal parts of the manubrium, the question 

 arises — Where are the nematocysts of the oral battery formed, 

 and how did they attain their position in this region ? An 

 answer is, I think, afforded by the study of the distribution 

 and arrangement of the nematocysts in the manubrial endo- 

 derm. The greatest number of these are to be found just 

 below the region of the gonad, where, in most specimens, 

 numerous thread-cells are to be met with among; the large 

 digestive cells of the endoderm. In this position one can 

 usually find a number of dark-staining interstitial cells, some 

 of which contain rudiments of stinging-capsules, and are 

 obviously nematoblasts (PI. 42, figs. 1 and 2). 



