OF A TETRAC0TYLIF0RJI LARVA TO A HOLOSTOMUM SP. 389 



development from the tetracotyliform larva to the sexually 

 mature animal. 



The supposition of the owl being one of the hosts of this 

 platyhelminth is the most probable, as von Linstow took his 

 specimens of H. excisum from two species of owl. 



The species of the family of Holostomidae are amongst the 

 handsomest of the Distomidae group, not only from the shape 

 of their bodies, but likewise from the internal anatomy, which 

 sharply separates them from the other species of Trematodes. 

 The peculiarity of a Holostomid is that in its development the 

 body undergoes a transformation, so that it is divided into two 

 separate bodies — an anterior and a posterior. 



Brandes recognises three types : 1st, the Leaf or Simple type 

 (Diplostomum longum) ; 2nd, the Spoon type (Haemastomum cla- 

 thratum) ; 3rd, the Goblet or Beaker type (Holostomum) ; but with 

 these types we need not at present concern ourselves. My object 

 is to take up von Linstow's Tetracotyla, and endeavour by means 

 of my own specimens to show concisely the development of this 

 stage after it has arrived at its final host. It was an accidental 

 but fortunate circumstance that called my attention to, and 

 suggested further investigation of, this subject, so that I can 

 take no credit for the results obtained, beyond that which may 

 be due for patient, sedulous work, in spite of the unpleasantness 

 and tediousness of the examination of the sedimentary sub- 

 stance from the alimentary tract. It was whilst so engaged in 

 re-examining the various objects that had been selected from my 

 precipitating pans, amongst which were specimens of this beautiful 

 forin of Trematoda, that I was struck with the similarity of some 

 minute plasmic forms to von Linstow's fig. 1 of Tetracotyla 

 typica (Plate 29, Fig. 17) ; so the remainder of the contents of the 

 intestine of this particular teal was carefully examined, and by this 

 means I was enabled to build up and mount on a single slide the 

 progressive stages of the development of this platyhelminth (a 

 Holostomum) from the point at which von Linstow leaves it, and at 

 which Brandes' feeding experiment failed him.* In other words, 

 I have demonstrated the development and growth of the different 

 stages from the Tetracotyla to the sexually mature animal. 



Besides the teal, I have found the Holostomidae parasitically 

 in the wild duck, wigeon, jay, blackbird, and starling. 



* This slide was exhibited at the meeting of March 5th, 1909. 



