385 



ON HOLOSTOMUM EXCISUM (LINSTOW, 1906), AND THE 

 DEVELOPMENT OF A TETRACOTYLIFORM LARVA 

 TO A HOLOSTOMUM sp. 



By T. B. Rosseter, F.R.M.S. 

 {Read March 5th, 1909.) 



Plate 29. 



Part I. 



In describing the method of fructification in Hymenolepis acicula 

 sinuata, in a footnote to my paper on that species of tapeworm, 

 I pointed out an affinity that existed between it and Holostomuni 

 excisuni, Linstow, in consequence of the method of transmission 

 of the spermatozoa, and the laurer canal existing in the Trematoda 

 and the functional uses of this organ as demonstrated by 0. von 

 Linstow in his description of Holostomuni excisum. It is not my 

 intention to enter into any explanation either by way of argument 

 or in substantiation of 0. von Linstow's diagnosis and description 

 of the anatomy of this Platyhelminth ; but as the accompanying 

 plate illustrates what I consider to be the final stage in the evolu- 

 tion of a Holostomuni (and which at the outset I would remark 

 is the object of my paper), it is my intention to give a condensed 

 translation of O. von Linstow's researches, and a description of 

 his new species of Holostomuni. Perhaps, therefore, some apology 

 is due from me to the members of the Quekett Club in general 

 and 0. von Linstow in particular. There are points in the 

 anatomical details to which objection might perhaps be taken, 

 but such a course would, under the circumstances, be unjustifiable 

 in this article. I may say that in the matter of the laurer 

 canal, as applied to the Holostomidae (consequently the Trema- 

 todae) by von Linstow, I am quite in accord with him. Von 

 Linstow took this species of Holostomuni from the intestine of 

 Aegolius otis and Strix Jlammea, two species of owls. 

 His description concisely translated is as follows : 

 " Body 3*17 mm. long ; anterior portion 1*06 mm. long, 0"99 mm. 

 broad. The back portion is curved, and the posterior or tail end 

 is rounded. 



Journ. Q. M. C, Series II.— No. 64. 29 



