Pit)}'. C. Gegcnbaur on Trachelius o\ uui. 201 



opcrculiiiii aiul organs of the senses show themselves. At this 

 time the vehim has reaehed its greatest develoj)meut, and it then 

 gradually diininislics. 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 C]uits the caj)sule. 

 When the velum has conij)letely disappeared, and the triturating 

 ])late and lingual cartilage have made their appearance, the cap- 

 sule opens and the little Neritina escapes, to live henceforward 

 in freedom. It creeps about uj)on the Dreissena whose shell 

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

 ganisms which now serve for its nourishment instead of its 

 sister-yelks. 



XXI. — Observations ou Traehelius ovum, Ehrenhery. 

 By Professor Carl Gkgenbauu*. 



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

 at the first glance, I took to be Traehelius 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 Dujardiu. 

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

 " intestiue^^ 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 oO 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 Traehelius 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, v.hich 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 ditFerent form in different 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 



* TranslatLtl bv W. S. Dallas, F.L.S.. from Miiller's Archiv. June 1S57, 

 p. 9. 



