954 SUMMARY OF CURRENT RESEARCHES RELATING TO 



introduction is followed by an account of tbo anatomy and life-history 

 of the common livcr-fluko, and that by a few words on pathological 

 and economic relations. A sketch is given of the generally received 

 systematic aiTangcmeut of the group ; in discussing the phylogcnetic 

 relations of the Trcraatoda attention is called to Fewkes's description of 

 a marine ccrcaria which had a tail distinctly annelid in character, 

 with bundles of bristles disposed at intervals along it. 



Aspidogaster conchicola.* — Herr A. Voeltzkow has investigated the 

 structure and life-history of the Treniatode Asjrklogas^ter conchicola dis- 

 covered by Von Bacr in the fresh-water mussel. His general results 

 are as follows: — The parasite occurs in the pericardium, the kidney, 

 and the red-brown organ of Anodonta and Unio. It lived four to five 

 weeks in a weak salt solution. The alimentary system consists of a 

 iirotrusiblo pharynx with salivary glands, and a sac-shaped gut with 

 amoeboid epithelial cells. The nervous system is well developed. The 

 sucker includes tasting organs and mucus-glands. The water-vascular 

 svstem consists of an expelling tube with a terminal bladder and foramen 

 and of the ciliated vessels tbroughout the body. The male side of the 

 reproductive system consists of testis, vas deferens, seminal vesicle, 

 prostate, penis sheath, and penis. The female system exhibits an ovary, 

 a " fallopian tube," oviduct and vulva, and also a triangular " ootyp " or 

 junction of fallopian tube, oviduct, and duct of the " yolk-receptacle." 

 There are two pairs of yolk-glands, two yolk-ducts ending in a yolk- 

 vesicle, which opens into the oviduct. Hitherto undescribcd is a special 

 recepfaculuvi vitcUi opening into the ootyp. There is no internal fer- 

 tilization. 



The differentiation of the perfect sucker from the embryonic structure 

 is accomplished by the development of transverse, median longitudinal, 

 and two external ridges. The ovum undergoes total segmentation. 

 As in other Trematodes an insheathing membrane is formed from cap- 

 shaped cells. The water-vascular system arises from the primitive 

 secreting organ. The essential reproductive organs are mesodennic ; 

 penis, vulva, receptaculum vitelli, and the associated ducts are ecto- 

 dermic in origin. The young animals enter the gut, pass their early 

 staf^es there, and pass through the gut, where it traverses the red- 

 brown organ and pericardium. In an appended paper, Herr Voeltzkow 

 discusses A. limacoides, a new species described by Diesing. 



HolostomuDi.t — Herr G. Brandos has a preliminary notice of his re- 

 searches on the genus Holostomum. A comprehension of its anatomy and 

 general form is not easy, as it has been reported to exhibit very different 

 arrangements from those generally seen in Trematodes. Linstow, for 

 example, has spoken of the dorsal as the ventral side. The author 

 explains the morphology of Holostomum by reference to the simpler 

 characters presented by Hemistomum. The former may be sliown to 

 exhibit the following characters : — The ovary lies in the anterior third 

 of the hind-body, and the paired testes are a little way behind it. The 

 oviduct, after some coils above the first testis, gives off the canal of 

 Laurer to the dorsal surface, then passes between the two testes, becomes 

 united with the unpaired yolk-duct, passes into the shell-gland, and 

 becomes a uterus. This extends as far as the anterior pole of the hind- 



* Arbeit. Zool.-Zoot. Inst. Wurzburp;, viii. (1888) pp. 249-292 (6 pis.), 

 t Zool. Anzeig., xi. (1888) pp. 424-6. 



