DURING HIS SOJOURN IN THE WESTERN PACIFIC. 533 



the same as Rudolphi's species. Diesing however includes these amongst the synonyms 

 of Monostomum trigonocephalum. 



E. Walter. Zeitschr. wiss. Zool. Vol. 56, 1893, p. 189. 



This paper includes a comparatively complete account of M. proteus Brandes and 

 M. reticulare van Ben., but the account of M. trigonocephalum is more meagre, so that 

 I have thought it worth while to print the following notes on the anatomy of this 

 form, but for many details I must refer the reader to Walter's paper. 



G. Brandes. Centrbl. Bakter. Vol. xii. 1892, p. .505. 



A. Looss. Zool. Jahrb. Syst. Vol. xii. 1899, p. 523. 



External Features, Ectoderm and Parenchyma. 



Since this article has been in type,' Professor A. Looss has published a most 

 valuable essay on the Trematodes of Egypt. He gives a short account of M. tiigono- 

 cephalum under the name Pronocephalus trigonocephalus {= M. trigonocephalum Rud. 

 partim) and a figure. With the exception of a few details his description agrees 

 with the following. 



Dr Willey brought back with him some portions of the intestine of a Ghelone imhri- 

 cata L. attached to which and half hidden in the mucous secretions were a small number 

 —some ten or twelve — Trematodes belonging to Rudolphi's species Monostomum trigono- 

 cephalum. The shape of these Trematodes varied markedly (Fig. la, lb, 1 c, Id, 

 Plate LIV.), some had an almost U shaped venti-al flexure, others were straight, but 

 all possessed the marked ventral hollow which caused van Beneden to describe the 

 species " excave comme un canot." The longest specimen would have measured some- 

 thing over 5 ram. had it been straightened. 



The body is covered by a cuticle of uniform thickness, this is apparently secreted 

 by extensions of certain cells which I take to be ectoderm and whose body with the 

 deeply stained nuclei are withdrawn some distance from the surface. Amongst these 

 cells run longitudinal and oblique fibres (Figs. 2 and 3, Plate LIV.) but I did not find 

 any absolutely transverse fibres : perhaps they are replaced by the diagonal fibres, which 

 are after all only slightly out of the transverse plane. Dorso-ventral fibres cross the 

 body in a vertical direction and are inserted above and below into the cuticle. They 

 often indent various organs, e.g. the testes, so as to destroy the evenness of their 

 surface. The solid parenchyma of the body consists for the most part of large cells 

 which tend to become very vacuolated (Fig. 3, Plate LIV.). These cells have minute 

 nuclei and the protoplasm stains very slightly. Every now and then a more compact 

 cell, better stained and with a larger nucleus, is met with embedded in the large 

 celled parenchyma. Such cells are especially common near the head where the looser 

 vacuolated cells are almost absent (Fig. 7). 



71—2 



