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IV. FuTtlier Researches on Tomopteris onisciformis, EschsehoUz. By William B. 

 Carpenter, WLI>., F.B.S., F.Z.S., F.G.S., and Edouard Claparede, M.D., 

 Felloio of the Physical Society of Geneva. 



ReadJanuary 19th, 1860. 



Having been fortunate enough to capture a considerable number of specimens of this 

 interesting Annelid during our joint sojourn at Lamlash Bay, Arran, during the month 

 of September last, and having been able to add much to the knowledge previously ob- 

 tained of its organization and reproduction, we have agreed to lay the results of our 

 observations before the Linnean Society, in the form of a continuation of the memoir 

 already communicated to it by one of iis, and printed in its Transactions (vol. xxii. p. 353). 

 Although we have miich to add, we find nothing to correct in any of the positive state- 

 ments of fact which that memou- contained ; and we have the satisfaction of bearing our 

 joint testimony, based on a renewed comparison of Mr. George West's delineations with 

 the objects from which they were taken, in regard to the truthfulness with which they 

 represent the conformation of this interesting animal*. 



In the first place, with respect to the specific diversity affirmed by Drs. Leuckart and 

 Pagenstecher t to exist between Tomopteris onisciformis and T. quadricornis, chiefly on the 

 ground of the presence in the latter of a pair of cephalic appendages not possessed by the 

 former, we have to state that the conviction already expressed by one of us % as to the 

 insufiiciency of this character has been fully borne out by our subsequent observations, 

 which have entirely satisfied us that the presence or absence of the appendages in ques- 

 tion depends solely upon the grade of development which the individual has attained. 

 We have been led, however, by certain minute differences between the organization of 

 the Tomopteris described by Leuckart and Pagenstecher, and that of the Tomopteris 

 which we have studied, to suspect that the forms we have severally described under the 

 designation T. onisciformis may not be specifically identical. 



The T. onisciformis and the T. quadricornis of Leuckart and Pagenstecher both possess 

 that remarkable pair of " frontal horns," projecting laterally from the most anterior part 

 of the head, which, as Mr. Huxley has remarked, give to the animal the aspect of a 

 hammer-headed shark ; and they both possess that pair of greatly elongated appendages 

 designated in the former memoir as the " styliform," but which we now prefer to term 

 the second antennce. These organs are far longer, relatively as well as absolutely, in the 



* In transferring these figures to copper, and in reducing their scale, the engraver has imparted to them a hard- 

 ness and stiffness which the originals do not possess ; and has also, by too deeply shading them, destroyed the effect 

 of transparency which the artist had aimed to give. 



t Miiller's Archiv, 1858, p. .588. % See vol. xxii., supplemental note in p. 362. 



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