MR 



ON SOME LOWER ANNELIDS. Gil 



development of a head. If this be a correct statement of the production of zooids in 

 Chatogaster, it would come under the last of the three groups into which Professor 

 Huxley some time since divided the phenomena of fissiparity in Vermes, namoly, that 

 in which " none of the segments of the produced zooid belonged to the parent stock--;i nd 

 the former contains hardly any of the primitive substance of the latter, being developed 

 by gemmation from its last segment." 



II. Remarks on Chsetogaster niveus, Ehrenberg. 



In some water containing conferva, from the river at Oxford, examined in May, I found 

 a Chcetogaster differing very greatly from that parasitic on the Liiinws, and identical, 

 I believe, with that figured by Ehrenberg in his 'Symbols Physical as Ch. whew. 

 This worm was hardly more than | inch long, thin and active, and apparently with a 

 firm, tense integument, very different, so far, from Ch. limncei. The whole worm was 

 much narrower and more elongated than that species, and by no means so transparent. 

 The prostomium (figs. 9 and 10) was longer and more obvious, the pharynx was longer 

 and apparently thicker in the walls, and the oesophagus was very much longer. The 

 vascular network on the intestine was more obvious in this species, though the other 

 vessels, segment-organs, and nervous system it seemed almost impossible to define. 



The most characteristic difference, however, was found in the bristles, which were 

 proportionally much longer and thinner, and quite different in shape; instead of 

 having a reflected apex, it was simply bifid, the point being very fine, and tin- bifid 

 structure very hard to see distinctly with a quarter-inch objective (fig. 11). In number 

 the bristles agreed with those of Ch. limncei. The mode of using the cephalic bristles 

 was much more rapid than in the parasitic species. The cephalic bundles were suddenly 

 thrown out laterally on either side of the head, and retracted, and thus worked up and 

 down, enabling the worm to move very rapidly. One specimen which I observed pre- 

 sented only five abdominal bristle-bundles, of which the two posterior were demarcated 

 as though belonging to a developing zooid. 



Ch. niveus is evidently fitted for a more active life than Ch. limncei ; but it differs from 

 Ch. diaphemus, which is non-parasitic, in the same particulars. The Ch. diastropltus oi 

 Gruithuisen may possibly be this species. 





III. iEolosonia quaternarium, Ehrenberg, and its embryonic form. 



Ehrenberg first observed JEolosoma in Dongola,— a wonderfully elastic, transparent, 

 spotted little worm, living in running waters ; he was afterwards astonished to find it 



O A ~ *~— — ^ 



near Berlin. I believe no figure or description of the worm has been published since 

 Ehrenberg's ■ Symbols Physicse/ 1828, excepting D'Udekem's account as to the gene- 

 rative glands*. The specimens I have examined were obtained by Mr. Charles Robert- 



* 



— ^„wy^ was written, x nave iounu a paper uy uujuig xix «*»»»»•• 



Anatomie,> 1865, in which he shortly describes two species of ^olosoma, one of which he identifies with the M 



termrium of Ehrenberg, and the other he calls £■. nlveum. 

 and 



his specimens 



appears to have had them under observation no longer than myself. In almost every particular our 



^ee, exceptin 

 VOL. XXVI. 



Professor Leydig speaks of the coloured 



4 u 



