1903.] On the Nematocysts of Solids. 473 



occurred in two of these specimens, and in none of the other fifty I 

 have examined. 



3. Two specimens of R. peregrina were placed in a large jar of sea- 

 water, with two amputated probosces of Cerebratulus urticans. They did 

 not take kindly to the diet, but, after several days, one had eaten 

 sufficient to fill its cnidophores with an inextricable tangle of the long 

 sinuous nematocysts of the nemertine, while the other had a few of 

 the same both in the cnidophores and in the " hepatic " diverticula. 



4. Two specimens of Spurilla neapolitana, which had nematocysts of 

 one sort only shown in fig. 8, were fed on Aiptasia variabilis, which 

 has two kinds of nematocysts, shown in fig. 7 ; the cnidosacs of the 

 Solids soon became crowded with the nematocysts of Aiptasia 

 (especially those of the acontia), but I was not able to continue the 

 experiment long enough to entirely replace the original form. Besides 

 the two forms of nematocysts mentioned, Aiptasia has a large number 

 of small spirocysts. These have a much more fragile appearance than 

 true nematocysts, and they must be destroyed and digested by the 

 gastric fluids of the ^Eolids, for I could not find any in the cnidophores 

 of these two specimens. 



In all these cases the nematocysts newly introduced did not simply 

 lie free in the lumen of the cnidosac, but were included in " cnido- 

 blasts " in the same way as those present in the ^Eolids at capture 

 (fig. 12). 



III. Function of Nematocysts and Cnidophores of Solids. 



If it is allowed that the nematocysts found in the cnidosacs of Solids 

 are of extraneous origin, and, in fact, are quasi faecal products of the 

 digestion of coelenterate prey, the question arises, " Is the elimination 

 of these inconvenient, and possibly dangerous constituents of the food, 

 the sole function of the cnidosacs and their associated mechanism, or 

 do they also serve as a means of offence or defence "1 The difficulty 

 of believing that the ^Eolid uses for its own purposes the very weapons 

 presumably " intended " to defend the hydroid from the ^Eolid and 

 other enemies, seems to have been the chief cause of Alder's scepticism 

 in regard to Strethill Wright's results. The nearest parallel I know 

 of is the case of the Cephalopod Tremoctopus microstore, described by 

 Troschel, and later by Joubin, as possessing nematocysts borne on special 

 cylinders on the arm. M. Bedot has proved by sections that these 

 cylinders are nothing more nor less than fragments of the arms of a 

 Medusa, and he remarks : " Nous avons, done, ici un exemple interessant 

 d'un animal empruntant pour sa defense les armes d'un autre animal, 

 caractere consider^ habituellement comme etant 1'apanage exclusif 

 <ie 1'homme." In this case, however, direct evidence of the use of the 

 nematocysts seems entirely wanting, and it is only the regular 



