60 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The food invariably consists of bloorl. The characters of the genus are 

 given in detail, with some account of species. The encysted forms have 

 not as yet been observed in Europe. 



Distomum cucumerinum Rud.* — Herr M. Braun has had an oppor- 

 tunity of studying Eudolphi's collection, and finds that this form is really 

 a Monoslomum, the ventral sucker being absent. The structure of the 

 internal organs entirely confirms this view. As to the species, though 

 nearly related to Mon. sarcidiornicola Megn., it seems probable that 

 Eudolphi's species is distinct, and must stand as Monostomum cucumeri- 

 num Bud. 



Trematodes from Snakes.f — Herr Walter Volz describes, under the 

 name of Distomum zschohhei, a new Trematode found in the lung of 

 Heterodon platyrhinus. He also notes briefly the occurrence of other 

 species of flukes in various snakes. 



New Species of Plectanocotyle.l— Dr. F. S. Monticelli describes 

 PI. lorenzii from the gills of a species of Trigla, adjacent to but readily 

 distinguishable from Diesing's PL elliptica. He suggests that it may 

 be found convenient to establish for the genus a distinct sub-family 

 {Exacotylinee) of Polystomidae. 



Development of Rhabdocoela.§ — Herr Ernst Bresslau publishes a 

 preliminary account of the observations made by him on the eggs of 

 Mesostomum ehrenbergi 0. Schm., HI. productum Leuck., and Bothromeso- 

 stomum personatum 0. Schm. The observations were made on summer 

 eggs, but winter eggs showed no striking differences. In M. productum 

 and B. personatum the egg contains a small germ-cell and a mass of 

 very numerous yolk-cells. The division of the germ-cell results in 

 the formation of a mass of similar blastomeres lying in the future 

 ventral half of the egg, beneath a dorsal mass of disintegrated yolk- 

 cells. In M. ehrenbergi the eggs are very small, and there are not more 

 than 40-50 yolk-cells. These are very speedily used up ; but from an 

 early stage the egg shows, in addition, large vacuolated cells which take 

 no direct part in the formation of the embryo. In this species also 

 there is a protective investment not present in the other forms. The 

 next change in all three forms is the formation of the rudiments of the 

 future organs. The cells arrange themselves into a plate-like structure 

 with a central spherical mass of cells. This spherical mass is the 

 primordium of the pharyngeal musculature, while from the disc of cells 

 the nervous system originates. In M. ehrenbergi the ectoderm is rapidly 

 differentiated from the ventral surface of the disc. It sends a solid out- 

 growth of cells into the primordium of the pharynx, and this out- 

 growth becomes the epithelium of the pharynx, which is thus truly 

 ectodermic in origin. In B. personatum the formation of ectoderm takes 

 place much more slowly, and the pharyngeal epithelium originates in situ 

 from the inner cells of the pharyngeal primordium. In 3f. productum the 

 development takes place in a fashion intermediate between these two 

 extremes. The further development is similar in all three forms. The 



* Zool. Anzeig., xxii. (1899) pp. 465-8. 

 t Arch. Natursesch.. lxv. (1899) pp. 331-40(1 pi.), 

 t Atti Accad. Torino, xxxiv. (1899) pp. 1045-53 (1 pi.). 

 § Zool. Anzeig., xxii. (1899) pp. 422-9 (4 figs.). 



