234 SUMMAEY OP CUKKENT BESEARCHES RELATING TO 



musculature of tte penial sheath a part of the ductus ejaculatorius is 

 evaginated, until at last the cirrus projects from the genital sinus ; 

 this is probably approximated to the orifice of the genital canal. 

 Self-impregnation through the uterus would appear to be possible. 



After an account of the remarkable " tail " of Bucephalus, the 

 author passes to the life-history of the two forms. The embryo which, 

 by unknown means, reaches the Anodonta or Unio, becomes there 

 several centimetres long, and gives off lateral branches ; the body- wall 

 is thin, and comparable to the parenchyma of the body ; within are 

 found BucepJiali of various stages of development, and arranged in 

 groups. The BucepJiali escape from the mussel by the anal siphon. 

 After swimming about for some hours, the cercarias sink to the bottom, 

 and, to undergo further development, they must now enter a suitable 

 host ; in the neighbourhood of Strassburg this is ordinarily Leuciscus 

 erytliropJithalmus (the Eudd) ; the cysts lie in the connective tissue 

 under the skin, and the containing capsule appears to be very thin 

 and elastic. During the period of encapsulation the animal grows, its 

 water-bladder becomes swollen out and filled with highly refractive 

 spherules, which are probably the final products of metabolism, the 

 stomach becomes relatively smaller, and the anterior sucker and 

 generative organs are developed ; the spines become larger and more 

 distinct. If the host fish is eaten by another fish the encysted animals 

 are set free and become sexually mature in the intestine of their new 

 host ; but experiments are still wanting to complete this part of the 

 life-history of these parasites. 



Development of Dendrocoelum lacteum.* — J. Jijima finds this 

 Planarian to be sexually mature once only during its life ; the ova 

 contain an immense quantity of yolk-cells, and 24 to 42 embryos are 

 to be found in one cocoon, whereas Metschnikoff only found 4 to 6 

 in Planaria polychroa. The ova appear to remain for a month 

 or six weeks in their cocoon ; this much longer period, as compared 

 with the ten days of P. polychroa, is thought to be due as much to 

 differences in temperature as to those of species. The segmentation 

 is total; the solid morula has a peripheral layer of cells which 

 seemed to be fused together, and an internal mass in which the form 

 of the blastomeres is still recognizable ; as these latter multiply the 

 bounding layer increases in thickness, while the free nuclei become 

 more abundant ; in fact, there appears to be a process of proliferation. 

 "When the embryo is 0*2 mm. in diameter the ectoderm may be seen 

 to be formed by a certain number of flattened cells, and the yolk-cells 

 are then separated from the embryo. The author agrees generally with 

 Metschnikoff in his account of the formation of the pharynx. From 

 the fifteenth to the eighteenth day the yolk-cells inclosed in the 

 cocoon are absorbed by the embryo, which may now be one millimetre 

 in diameter ; the pharynx undergoes degeneration and its place is 

 taken by the cavity of the proboscis ; a short time before it leaves 

 the cocoon an oral orifice is developed. Like Metschnikoff, Jijima 



* Zool. Anzeig., vi. (1883) pp. 605-10. Also Bull. Sci. Dep. Nord, vi. (1883) 

 pp. 100-5. 



