464 G. H. PAEKER 



has long been recognized and much has been written about their 

 method of development and the means by which they are ex- 

 ploded. It is not my intention to take up a discussion of these 

 problems but to limit myself to the single question of the rela- 

 tion of the nematocyst to the nervous mechanism of sea-anemones 

 as seen in normal activity. 



In 1871 Schulze showed that when the nematocysts in Cordy- 

 lophora were discharged by impact with a foreign body this 

 discharge took place only at the spot where the foreign body 

 came in contact with the animal. Schulze showed further that 

 the nematocyst cells were provided with a small bristle-like 

 structure, the cnidocil, which projected beyond the general sur- 

 face of the animal and served as a trigger for the explosion of 

 the nematocyst itself. Some eight years later the Hertwigs 

 ('79-80) discovered branched basal processes on the cells which 

 produce the nematocysts and believed these to be nervous in 

 function. Thus it came to be assumed that under appropriate 

 nervous stimulation large numbers of nematocysts could be 

 discharged in moments of need. This theory of the nervous 

 discharge of the nematocysts was supported from one stand- 

 point or another by von Lendenfeld ('83), Chun ('91), Schneider 

 ('02), Wolff ('04), Groselj ('09) and Baglioni ('13), while other 

 investigators were rather inclined to accept some of the various 

 modifications of the theory of non-nervous discharge as originally 

 advanced by Schulze. Metridium offers some excellent oppor- 

 tunities for testing these two general views. 



Several types of nematocysts occur quite commonly in the 

 ectoderm of Metridium. Small cysts with short slender fila- 

 ments occur sparingly on the mesenteric convolutions and in 

 the ectoderm of the column wall. Large ones are found scattered 

 over the oesophagus. But the regions in which the nematocysts 

 "are especially developed are the tentacles and the acontia. 

 On stimulating the tentacles with dilute hydrochloric acid, great 

 numbers of rod-like bodies about 20/x in length together with 

 many fine filaments at least 140yu long are discharged. On 

 similar treatment of the acontia, a perfect forest of nettle fila- 

 ments are discharged. These come from capsules about 45ai 



