On the Specific Characters of Asplanchna intermedia, Hudson. 



By Charles F. Eousselet, F.R.M.S. 



{Bead November UtJi, 1900.) 



Plate 1. 



The object of this paper is to elucidate the differences which 

 exist between A splanchna intermedia and the closely allied species 

 Asplanchna hrightwelli. 



Dr. Hudson, in the supplement to his monograph of the 

 Rotifera (p. 12), writes that Mr. Gosse agreed with him in saying 

 that he could not distinguish the female A. i7itermedia from that 

 of A. hrightwelli. 



The reason of this, I think, is that in two essential points 

 A. hrightv)elli has from the beginning been incorrectly described, 

 and I suspect that the early observers had, without knowing it, 

 sometimes the one and sometimes the other species under obser- 

 vation, and so mixed up the characters. 



These two species are, however, readily distinguished from each 

 other by the following three points, any one of which is sufficient 

 for identification : (1) The shape of the jaws ; (2) The number 

 of flame-cells (vibratile tags) ; (3) The shape of the male. 



The figure of the jaws of A. hrightioelli, which Dr. Hudson has 

 given on PI. XII., Fig. 1, c, of his monograph, is unfortunately 

 quite wrong, and has led to further errors. This figure has been 

 reproduced from John Dalrymple's paper of 1849, evidently 

 without being verified ; and Mr. Dalrymple seems to have copied 

 his figure from Mr. Brightwell's paper of 1848, or else Mr. 

 Brightwell must have supplied him with two diflferent species of 

 Asplanchna, On comparing this figure with the jaws of A. 

 amphora., it becomes evident that, when drawing these jaws, both 

 Brightwell and Dalrymple must have chanced to have had a 

 specimen of A. amphora under their microscopes, while their 

 drawing of the male is undoubtedly that of A. hrightwelli. 



These various observations may have been made at different 

 times, as Brightwell states that he found his animal several times 

 during seven years. It is quite possible also that the two species 

 were present in the pond simultaneously. In the " Supplement '' 

 in 1889 Dr. Hudson has given another and more correct figure of 



