728 RECORD OP CURRENT RESEARCHES RELATING TO 



stalk of about h mm. in length, and is attacliecl to tlie gill-lamella of 

 the abdominal ajipendages of tbc king-crab. 



Classification of the Monogenetic Trematoda.* — It is to Dujardin 

 that zoology owes the first classification of the Trematoda, which 

 name was first used by Rudolphi (l>-08-1810). The French naturalist 

 recognized three families, and his work has been subjected to changes 

 at the hands of his successors ; it was not, however, till 1861 that a 

 really natural classification of these forms was put forth by IM. P. 

 van Beneden, who recognizing and giving the proper weight to 

 the striking differences to be observed in their modes of genera- 

 tion, divided the Trematoda into the Monogenea and Digenea. In 

 addition to the five families formed by Van Beneden and Hesse, Dr. 

 Taschenbcrg now proposes two new ones, Monocotylidie and Micro- 

 cotylida) ; and divides the Monogenea into two families of Tristome^B 

 and Polystomete, which differ in the following points : in the former 

 the anterior end of the body is not narrowed, there is no terminal 

 sucker, and the ova are only provided with a filamentous appendage 

 at one pole, while in the latter there is a large posterior sucking 

 disk, the body is elongated and narrower anteriorly, while the ova 

 frequently have two filamentous appendages. 



Entoparasitic Marine Trematodes.f — An account of the mor- 

 phology of several sjjecies is given by A. Villot. 



The author recommends hardening the specimens in absolute 

 alcohol, imbedding in glycerine soap, staining the sections with picro- 

 carmine or ha3matoxylin, clarifying with oil of cloves or creosote, and 

 mounting in balsam. 



He describes three species of Distomiim, one of Monostomum, one of 

 Holostomum, and six of Cercaria, for the details of structure of which 

 we must refer to the paper itself, confining ourselves to the point of 

 chief morj)hological interest, namely, the account of the vascular 

 system as observed in Distomutn inslgne, a large species, found in the 

 digestive canal of the elasmobranch Echinorhinus sp/nosMS. 



The vascular system in this species consists firstly of a Y-shaped 

 contractile vessel, opening posterioidy by a terminal pore, and 

 secondly, of a capillary network, permeating the tissues and anasto- 

 mosing at intervals, forming true sinuses. These dilatations are espe- 

 cially abundant just beneath the integuments in the outer layer of 

 parenchyma, where they form a distinct layer, presenting the appear- 

 ance in cross section of a multitude of cells, for which, indeed, they 

 have often been mistaken. 



Villot considers that this apparatus is both excretory and cir- 

 culatory in function, the office of excretion being assigned to the 

 contractile vessel, while the extensive system of capillaries and sinuses 

 serves for the transport of nutrient matter from the alimentary canal to 

 the various parts of the system ; and he remarks that we have here 

 "a fresh example of the tendency to the accumulation of functions, 

 which always accompanies the degradation of the organism," and 



* ' Zeitschr. ges. Natm-w.,' lii. (1879) p. 232. 



t ' Ann. Sci. Nat. (Zool.),' viii. (1879), No.s. (2-3). 



