ON THE DEVELOPMENT AND MIGRATIONS OF THE ENTOZOA. 115 



perished or had been devoured by Entomostraca present in the jar ; others 

 were found at the bottom of the vessel inactive, stretched out, and apparently 

 dead. By this time (December 2nd, 1862), the development of the salt- 

 water ova had much more advanced ; the yelk had, in many instances, 

 become transformed into embryos more or less complete, and several of 

 the latter had quitted their shells. On the 13th of April these embryos 

 had acquired well-marked digestive organs, and I thought I could discern 

 the rudiments of an internal reproductive apparatus. They now exhibited 

 a condition corresponding with that which the freshwater embiyos had 

 obtained at so early a period as the 7th of November. In other words, the 

 freshwater embryos at one month (after immersion of the ova^ were as far 

 advanced as the salt-water embryos at six months. I do not attempt to 

 explain this ; I can only speak to the facts as they were presented. On the 

 16th of July, 1863, all the freshwater embryos had disappeared ; a few dead 

 ova, with dark granular contents, lay at the bottom of the jar ; and there 

 were a great number of empty shells, with parasitic algoids growing from 

 their outer surfaces. In the salt water, on the 23rd September, 1863, there 

 were stiU many eggs containing segmented yelks, and others -with fully formed 

 embryos, these being likewise associated with mmaerous free living embryos. 



On the 2.5th of April, 1864, I still found some embryos aUve in the salt 

 water ; but I could not discover any traces of the original eggs. The move- 

 ments of the young worms were tolerably free, the largest specimen 

 measuring about -^^ of an inch in length. 



A careful search, made on the 21st of July last, failed to reveal any 

 evidence of their existence ; but as it is quite possible that one or two may 

 stiU. be living, I have retained the contents of the jar for subsequent final 

 examination. 



7. Ascaris marginata. — On the 25th February, 1863, a quantity of eggs 

 were taken from the uterus of a full-grown female, and placed in fresh 

 water supplied vjii^i Anacharis. On the 16th of Jiily following, most of the 

 ova appeared to contain embryos, which were moving freely within their 

 shells ; but none were foimd to have escaped. On the 23rd September, 1863, 

 similar facts presented themselves ; and although I detected no free embryos, 

 there were, nevertheless, several empty egg-shells at the bottom of the 

 vessel. The same conditions were still observed on the 20th April, 1864 ; 

 but when I last examined the water (July 21, 1864), one or two embryos 

 were found free. 



8. Ascaris lumhricoides. — On the 8th December, 1862, a large number of 

 ova were placed in a jar containing fresh water. By the 13th of March 

 many of them appeared to have reached an early stage of embryonic forma- 

 tion, and then to have perished. 



9. Ascaris megalocephala . — On the 24th of April, 1863, several thousand 

 eggs, in some of which yelk-segmentation had commenced, were placed in 

 two jars containing fresh water and Anacharis. On the 17th of the follow- 

 ing July, a large proportion of the eggs were found to inclose well-developed 

 embryos ; but none were observed free. On the 23rd of September, not only 

 were there a quantity of empty shells in both vessels, but also a correspond- 

 ing number of free embryos, some of which appeared to have grown con- 

 siderably since quitting the egg. 



On the 18th of July, 1863, some of the immature eggs, as well as eggs 

 containing embryos, were placed in a small vessel containing pond-mud 

 (thin clay). On the 23rd September following, I found the mud to contain 

 many eggs still undergoing yelk-segmentation, others with immature em- 



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