142 DR. T. S. COBBOLD ON SOME EXPEBIMENTS WITH ENTOZOA. 



men liver-fluke in water led to the formation of incompletely de- 

 veloped embryos within the space of ten weeks. At the furthest 

 stage observed the embryos were ovoid, slightly constricted here 

 and there, some of them displaying traces of a rudimentary 

 eye-spot. 



6. Ascaris osculata. — Eggs, with commencing yelk-segmentation, 

 placed in " fresh " water developed into free embryos in less than 

 three weeks ; while those deposited in salt water required a period 

 of six months for the completion of their development. At the 

 expiration of twenty months the largest examples did not exceed 

 Jjjth of an inch in length. 



Eggs of this nematode with segmented yelks, also eggs con- 

 taining embryos, and likewise many free embryos were adminis- 

 tered to two dogs without producing a positive elTect. The same 

 result followed their introduction into the intestinal canal of frogs 

 and various fishes. In the case of one gold-carp, however, nume- 

 rous empty egg-shells were found, testifying to the escape of the 

 embryonic contents. 



7. Ascaris marginata. — Immersion of the eggs of this species 

 led to the completion of their embryonic development within the 

 chorion at the expiration of a period of four months ; nevertheless 

 nearly seventeen months elapsed before the embryos quitted their 

 shells. 



8. Ascaris lumbricoides. — In this species the deposition of the 

 ova in fresh water gave no satisfactory result. At the expiration 

 of three months the eggs had, from some unascertained cause, 

 lost their vitality. The egg-contents had not completed their 

 embryonic formation. 



9. Ascaris megalocepTiala. — In this closely allied form, intra- 

 chorional embryonic development was fully perfected within the 

 space of three months after immersion; and in less than five 

 months many of the embryos were found to have quitted their 

 shells. 



10. Oxyuris vermicularis. — Eggs of the thread- worm contain- 

 ing the characteristic tadpole-shaped embryos failed to liberate 

 their contents either in water, in decaying fruit, or iu other vege- 

 table matters, although retained in these media for several months. 

 The experiments were several times repeated, but, in all cases, 

 the ova perished. In like manner, the administration of the eggs 

 of this species, with their contained embryos, in one case to a 

 monkey, and in another to a goat, yielded only negative results. 



11. Strongylus armatus. — As in the case of the common human 



