:\hmi<r}^ Prof. C. Gejirenbaur on Trachelius ovum. 201 



operculum and organs of the senses show themselves. At this 

 time the velum has reached its greatest development, and it then 

 gradually diminishes. The tentacles first appear as small tu- 

 bercles close to the eyes, and gradually increase until they form 

 distinct tentacles by the time the animal quits the capsule. 

 When the velum has completely disappeared, and the triturating 

 plate and lingual cartilage have made their appearance, the cap- 

 sule opens and the little Neiitina escapes, to live henceforward 

 in freedom. It creeps about upon the Dreissena whose shell 

 bore its egg-capsule, and finds upon this the microscopic or- 

 ganisms which now serve for its nourishment instead of its 



sister-yelks. ■^"'''''' '^' -'h'''*- " ■' •. ■ -f '^"'j. 



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XXL — Observations on Trachelius ovum, Ehrenbergy^^,\ ofjj 

 By Professor Carl Gegenbaur*. !. ffoH 



In the course of last November I met with an Infusorium, which, 

 at the first glance, I took to be Trachelius ovum. Of this, how- 

 ever, I soon began to entertain doubts, although I could discover 

 no known form with which there existed any agreement. For 

 this purpose I could only consult Ehrenberg and Dujardin. 

 The outlines agreed with Trachelius ovum, and the form of the 

 '* intestine" also was in general the same as in that species. 

 The longitudinal series of cilia, however, were far more nume- 

 rous; and beneath the cuticula, in the walls of the body, a great 

 many vesicles, arranged at regular distances apart, lay imbedded : 

 with a moderate magnifying power, these looked almost like nu- 

 clei, but they were really contractile organs. I reckoned their 

 number at from 50 to 60. They were not spherical, but discoid ; 

 they contracted very slowly, and out of about ten which might be 

 watched at the same time, I never found more than one or two 

 in action. In Ehrenberg's figure of Trachelius ovum, something 

 is represented that may be referred to these organs. A little 

 above the middle of the body there is a large, richly ciliated 

 cleft, which I regard as the mouth. It leads by a pouch-like 

 prolongation, which is also ciliated, into a finely granular organ, 

 which passes through nearly the whole length of the animal, 

 and which possesses a very different form in difierent specimens. 

 This part never lies in the middle of the body, but always nearer 

 to the side on which the buccal slit is situated, where it is also 

 partially amalgamated with the wall of the body. Numerous 

 processes, consisting of hyaline or finely granular substance, 

 issuing from this "intestiniform" organ, penetrate the cavity of 



Translated by W. S. Dallas, F.L.S., from MuUer's Archiv, June 1857, 



p. 9. 



