262 Martin, A Note on the Occurrence of Nematocysts and Similar Structures etc. 



There are two other cases amongst the Rhabdocoelida which 

 I am inclined to refer with a certain amount of hesitation to this 

 category, and those are the cases of Nematocysts in Allostoma 

 monotrochum and Ulianinia mollissima. 



The Nematocysts of Allostoma monotrochum were described by 

 von Graff in the following passage. 



,,Von Allostoma monotrochum Graff wurden (409, pag. 406, 

 XIX, 19, b), zu je 3 4 in einer Epithelzelle eingeschlossen 3 4 w 

 lange ovale Nematocysten bieschrieben, die einen spiral aufgerollten 

 Faden zu enthalten scheinen. Doch bedurfen diese, wie auch die 

 ,Corpuscnla bacillaria cava (organa uriicatoria?) multa 1 des Pro- 

 vortex puuctatns (Levins.) (368, pag. 179) erst noch einer genauen 

 Untersuchung." 



In this connection it is interesting to observe that Ritter- 

 zahony in his ,,Beitrag zur Anatornie von Allostoma monotrochum 11 

 states on this subject. - 



,,Nesselkapseln (Nematocysten). die von Graff fur A. mono- 

 trochum beschrieben worden sind (2, p. 406), vermisste ich jedoch.-' 



On one occasion, in May 1908, I saw an Allostoma monotrochum 

 crawling with its proboscis extended over a Campanularia, and in 

 this case the Allostoma monotrochum contained Nematocysts which 

 agreed in appearance with those of the Campanularia. 



The Nematocysts in Ulianinia mollissima were first described 

 by Levinsen. In his Monograph on the Turbellaria, von Graff 

 has renamed this form Cylindrostoma mollissima and therefore in 

 his new nomenclature, I suppose the correct name would be 

 Pscndostoma mollissima. I have not unfortunately been able to see 

 the original description of this form, but von Graff states on 

 page 2042 of his account of the Turbellaria in Bronn's Tierreich. - 



,,Nesselorgane gleich jenen des Microstomum line-are werden 

 fur Ulianinia mollissima Levins. (368, p. 195) beschrieben." 



and on the strength of this statement I am inclined to regard 

 these structures as Cleptocnidae. 



As far as I am aware there is no instance of the occurrence 

 of Nematocysts in the Triclads and only two in the Polyclads, 

 viz., in Stylochoplana tarcla and Anoitynuts n'rilis. Stylochoplana 

 tanla has as far as I know only once been found by von Graff, 

 at Trieste. It is interesting to observe that it only differs from 

 the common Stylochoplana fusca by its slightly smaller size, sluggish 

 habits, and the possession of Nematocysts. The Nematocysts have 

 not been figured, but are described as structures 0.01 mm long, 

 with a thread 0.015 mm long, the base of the thread being covered 

 with spines for a distance of 0.009 mm. This Nematocyst appears 

 to be a very common type of Coelenterate Nematocyst, and it is 

 tempting to regard these structures in Stylochoplana tarda as 



