1903.] On the Nematocysts of Solids. 471 



6. The Ciliated Canal between the Gastric Diverticula and Cnidosac : 



The existence of this canal, as mentioned above, was first established 

 hi transparent pupillse by Hancock and Erableton, and subsequently 

 by means of serial sections by Herdman and Clubb and others ; but 

 its function has always remained a mystery. Hecht suggested that it 

 might act as a safety valve, to allow the escape of superfluous 

 nematocysts from the cnidosac. Krembzow combats this view and 

 maintains that the function of the canal is to allow the passage into 

 the cnidosac of nematocysts developed in the " liver cells." Though 

 there is no better evidence for the development of cnidsein the " liver " 

 than there is for their development in the cnidosacs, this view is 

 certainly more in accordance with observed facts than the former. For 

 as Hancock and Embleton observe, the cilia on the walls of the canal 

 cause a current towards the cnidosac ; these naturalists also note that 

 particles of various sorts, "accidentally pressed into the canal," are 

 carried into the cnidosac. Trinchese (1) actually observed the passage 

 of nematocysts in this way,* but, like Hancock and Embleton, he con- 

 sidered this a purely artificial effect. He notes that the cnidse so 

 passing are sometimes like those already in the cnidosac, sometimes 

 different, and remarks : "In ambo i casi esse appartevano ad individui 

 mangiati dal suddetto animale (Facelina sp.); nel primo caso esse 

 appartevano a qualche Facelina, nel secondo ad ^Eolididae di altri 

 generi." It is curious that he does not consider the possibility of their 

 derivation from Ccelenterate prey. I have also observed the passage of 

 nematocysts through the canal, and certainly in this case they belonged 

 to a hydroid (Pen. Cawlinii) devoured a short time before. 



The ciliated canals and cnidosacs have of course no power of distin- 

 guishing nematocysts from other small indigestible bodies. Thus Hecht 

 observed that when some Facelina cwonata had been feeding on Elysia, 

 the radular teeth of the latter appeared in the cnidosacs of the Facelina. 

 I have observed the same thing in the case of F. Drummondii which had 

 devoured two small specimens of R. peregrina. Probably the batonnets 

 mentioned by Vayssiere as occurring in the cnidosacs of Flabellina affinis 

 and other species of ^Eolids,t are due to the individuals in ques- 

 tion having varied their diet by devouring some spiculiferous 

 organism. 



Experiments. Strethill Wright's most conclusive evidence for the 

 extraneous origin of nematocysts in ^Eolidse was his experiment of 

 feeding an E. (Facelina) Drummondii, having Tubularia nematocysts in 

 its cnidosacs, on Campanularia Johnstoni, the nematocysts of which 

 subsequently appeared in the cerata of the ^Eolid. I have carried out 

 similar experiments on a number of individuals of two species of ^Eolids, 



* Part II. p. 53. 

 f Loc. cit,, p. 82. 



