238 Prof. Ehlers on the Development of Syngamus trachealis. 



of 0*036 millim. A distinctly double-contoured shell forms the 

 external envelope : it exhibits at each pole a circular gap ; but 

 even here the entrance to the interior of the ovum is closed by a 

 very fine membrane, which adheres closely to the inner surface 

 of the shell throughout. In the centre of the ovum the dark, 

 segmented vitellus lies in a clear, apparently fluid, substance ; 

 in this stage it is 0*084 millim. in length. Such ova I put 

 into earth which was kept moist, or into dung, or into water 

 with or without an intermixture of mucus from the trachea of 

 the birds, or other portions of animal tissue. Here the ova were 

 developed, whether the materials did or did not fall into a state 

 of strong decomposition. The only variation was in the dura- 

 tion of the development, evidently chiefly in dependance on 

 the temperature ; for ova which I had set aside for develop- 

 ment in an unwarmed room on the 20th September, presented 

 no change for a long time at first, and it was only on the 27th 

 October, when the room was permanently heated, that young 

 worms, rolled into several convolutions, were developed in 

 them. In another case, when the room was kept at a uniform 

 temperature, the ova were developed in the same way in eight 

 days. From a number of ova, although always comparatively 

 few, the young worms escaped at one of the poles of the ovum, 

 where the circular gap existed in the firm egg-shell. The 

 free young worms were filiform, with a blunt head and a 

 pointed tail ; the anterior third of the body was translucent ; 

 but further on there was a finely granular mass. They were 

 always enveloped by a sheath-like, clear, and extremely fine 

 membrane, which could also be recognized on the young still 

 remaining in the ovum. During this hatching many of the 

 animals died, from not being able completely to quit the egg- 

 shell. Those which acquired their freedom usually moved but 

 sluggishly; and I have been unable as yet to trace their further 

 development. This is evidently only an exceptional case, but 

 still worthy of notice. The majority of the ova remain in a 

 condition in which the young worms developed in them, which 

 now occupy the whole space within the egg-shell, lie quietly 

 or make but few movements. This is not the place to enter 

 upon the details of the development; and it will sufiiceto state 

 that the development in general takes place as in other para- 

 sitic Nematodes. 



I made feeding-experiments with ova developed in the 

 above manner. A cole tit [Parus major) j which I had long 

 observed in a cage in order to convince myself of its good 

 health, received, on the morning of the 3rd November, in a 

 drop of water, a great number of the ova in which the em- 

 bryos were developed. On the evening of the 20th November 



