Royal Society. 529 



example, treated by the former rule, we may consider the per- 

 mutation 1212 derived from the primitive arrangement 1122. 

 Considering this primitive arrangement as a particular case 

 of abcd^ there are four permutations which, on the suppositions 

 a — h= 1, c=rf = 2, reduce themselves to 1212, viz. acbd^ bead, 

 adbc, bdac, which are obtained by means of the respective 

 symbols {a){bc){d)', {abc){d); {a){bdc)\ (abdc), the supplements 

 of the exponents of irregularity being therefore 1, 2, 2, 3, or the 

 permutation being negative; in fact it is obviously derivable 

 by means of an inversion of the two mean terms. 



58 Chancery Lane, 

 June 1849. 



LXXVIII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from p. 469,] 



Feb. 22, T^ESCRIPTION of an Infusory Animalcule allied to 

 1849. -^-' the genus Notommata of Ehrenberg, hitherto unde- 

 scribed. By John Dalrymple, Esq., F.R.C.S. 



The examination of various specimens of the animalcule described 

 by the author, disclosed the dioecious character of one of the more 

 highly organized of the rotiferous class of Infusoria, hitherto sup- 

 posed to be androgenous. This discovery was first made by obser- 

 ving the difference in the form and development of the embryo 

 while still enclosed in the ovisac of the parent animal. From the 

 extreme transparency of this form of rotifer, it is possible to trace 

 the progressive development of the young from the Graeffian vesicle 

 in the ovary to the period of mature gestation, when the embryo is 

 expelled, the whole machinery of whose organs has been perfected 

 while still within the body of the female. 



Thus, although the young one observed in the ovisac, when nearly 

 ready to be expelled, was in the great majority of instances a mi- 

 niature portrait of the parent, yet occasionally an embryo was seen 

 of a different aspect, within whose body a vesicle was discovered 

 filled with actively moving spermatozoa. 



A further investigation of the subject brought clear evidence of 

 the functions performed by this male, — its copulation with the young 

 females; but it also displayed the singular fact, that although the 

 organs of reproduction and locomotion were highly developed, there 

 was a total absence of those of assimilation ; in fact, that neither 

 mouth, nor stomach, nor other digestive cavity or glands, were pre- 

 sent in its curious organization. 



In the early part of the paper the author describes the anatomy 

 of the female, which differs from the family of Notommata of Ehren- 

 berg, in the absence of intestine and anal orifice, and forcipated or 

 caudal foot. In every other respect the organization is so similar to 

 that class, that the author believes the proper place for this animal- 

 cule to be in a sub-genus of Notommata. 



Phil. Mag, S. 3. No. 232. Suppl. Vol. 34. 2 M 



