ox THE SCOLEX OF A CESXODE. 73 



5. On the Scolex in the Oestode Genus Dutldersia, and on 

 the Species of that Genus, ^y Frank E. Beddard, 

 M.A., D.Sc, F.R.S., F.Z.S. 



[Received December 15, 1916 : Read February 6, 1917.] 

 (Text-figvires 1-5.) 



Index. p^^g^, 



Duthiersia Jimhriata Diesiug 79 



D. expansa Perrier 80 



The genus Duthiersia is fairly well known to us from the 

 investigations of authors whose several contributions are qvioted 

 later *, but there still remain a few points to which attention 

 has not yet been directed, or concerning which thei-e is up to the 

 present some difference of opinion. 



Some little time since I had the opportunity of examining 

 living examples of the genus from the Nilotic Monitor, which 

 enabled me to ascertain a structural feature which has escaped 

 the attention of my predecessors —very probably because their 

 investigations were made upon preserved material only. The 

 scolices of several examples were in active movement, and from 

 the apex of the scolex was seen to protrude a finger-like process 

 which explored the surroundings. A more careful study of these 

 living worms showed that the apex of the scolex is occupied by a 

 circular pit, quite small like that of many species of Ichthyotcenia, 

 which is apparently eversible. This pit lies between the upper 

 extremities of the dorsal and ventral bothria, on a patch of 

 integument which is not invaded by the bothria. The area in 

 question is more extensive than the pit which occupies its centre. 

 Transvei-se sections confirmed the existence of this structure, 

 which has not yet been described in the genus Duthiersia. The 

 pit is so small that it only appeared in two sections of one series 

 which I prepared, and only in five of another (thinner) series. 

 And as these are naturally the very first sections of the series 

 and very small in area, the apical pit might be easily missed, and 

 possibly has been. 



The two series of sections I'eferred to were transverse. I have 

 also found the apical pit in horizontal sections through the scolex. 

 In all of these it appears as a mere pit ; certain special structures 

 (text-fig. 1, s) were to be observed in the shape of delicate filaments 

 arising from the margin of the pit, possibly of a sensoiy nature. 

 As to the protrusion of the entire apex of the papilla, I believe it 

 to consist of the tissues surrounding the pit as it was too large to 

 be a mei-e evei-sion of that orifice. But possibly the pit was also 

 everted, a fact of which I am not able to speak with certainty. 

 The apical pit appears to me to be of a sensory nature, and thus 



* Page 75, footnotes. 



