260 Martin, A Note on the Occurrence of Neraatocysts and Similar Structures etc. 



in the case of the Nematocysts of Otoplana sctosa described by 

 Du Plessis. Von Graff states on page 2042. 



,,Dieselben bilden lange und dicke Btindel, deren Spitzen iiber 

 die Oberflache der Haut vorragen. 'L'animal pent comme les autres 

 Monotes rejeter ces baguettes au dehors a volonte et sur les pre- 

 parations colorees au bleu d'aniline on voit que de chacune de ces 

 baguettes peut sortir un tres long filament. Ce sont done des 

 vrais nematocystes' (Du Plessis)." 



If this account is accepted it would appear that we have here 

 a case precisely analogous to that of the Pseudocnidae of the 

 Nemertinea which are described below. 



(b) Cleptocnidae. 



In this category I am inclined to place the instances of the 

 occurrence of Nematocysts in Microstomum lineare, Microstomum 

 rubroculatum, Microstomum giganteum, Microstomum papiUosiini, 

 Stenostoma Sieboldn, Pseudostoma mollissima and Allostoma mono- 

 trochum. 



The clearest case of the occurrence of Cleptocnidae in the 

 Turbellaria is that of the nematocysts of Hydra in Microstomum 

 linear e. 



"The Nematocysts of Turbellaria were probably first observed 

 by Oersted (13) in Microstomum lineare but he failed to recognise 

 their true character, and described them as 'krugformige Driisen'. 

 They were subsequently examined by von Siebold(17) in 1848, 

 and he leaves no doubt as to his recognition of their nature des- 

 cribing them as thread cells which 'denen der Hydra auf ein Haar 

 gleichen solltenV 



It is probably to the occurrence of these true Nematocysts in 

 Microstomum lineare that we owe the numerous accounts of Nemato- 

 cysts in Turbellaria given above, since it seems to have been felt 

 that the transitional stages between these true Nematocysts and 

 the ordinary Rhabdites of Turbellaria should be found. The proof 

 that these structures in Microstomum are Cleptocnidae depends 

 mainly on the following observations (vid. Q. J. M. S., Vol. 52, 

 1908). 



(1) Microstomum lineare was seen to feed readily on hydra. 

 Under these circumstances the three types of Nematocysts charac- 

 teristic of Hydra were found under the skin of the Microstomum. 



(2) Some Microstomum which had fed upon Cordylopkora lacustris 

 were found to contain the characteristic Nematocysts of Cordylo- 

 phora in place of those of Hydra. 



(3) In both these cases all the stages of the transportation of 

 the Nematocysts from the lumen of the gut to their definitive 

 position in the skin were found in sections of the worms. 



