430 MICROSCOPIC FORMS OF ANIMAL LIFE. 



by hollow stalks to the main tube, having a long cilium in the 

 interior of each, that is- attached by one extremity to the interior 

 of the sac, and vibrates with a quick uudulatoiy motion in its 

 cavity; and there can be little doubt that their purpose is to 

 keep up a constant movement in the contents of the aquiferous 

 tubes, whereby fresh water may be continually introduced from 

 without, for the aeration of the fluids of the body. 1 There 

 is much uncertainty with regard to the structures which Prof. 

 Ehrenberg has described as ganglia and nerves ; and it seems 

 doubtful if there is more than a single nervous centre in 

 the neighborhood of the single, double, or multiple red spots, 

 which are seen upon the head of the liotifera, and which, cor- 

 responding precisely in situation with those that in the higher 

 Articulata are unquestionably eyes, are probably to be regarded 

 as rudiments of visual organs. 



279. The Reproduction of the Rotifera has not yet been com- 

 pletely elucidated. There is no instance, in this group, in which 

 multiplication by gemmation or spontaneous fission is certainly 

 known to take place ; but the occurrence of clusters formed by 

 the aggregation of a number of individuals of Conochilus, adhe- 

 rent by their tails, and enclosed within a common lorica, would 

 seem to indicate that these clusters, like the aggregations of 

 Polygastrica, Bryozoa, and Tunicata, must have been formed by 

 continuous growth from a single individual. The ordinary 

 method of multiplication, however, is commonly supposed to be 

 by a proper generative act ; as distinct sexes have been disco- 

 vered in several individuals, and the act of sexual union has been 

 witnessed. The condition of the male of the remarkable genus 

 described by Mr. Dalrymple (loc. cit.) is a most extraordinary 

 one ; for it possesses no mandibles, pharynx, oesophagus, stomach, 

 nor hepatic glands ; having, in fact, no other organs fully deve- 

 loped, than those of generation. It would appear, therefore, 

 quite unfit to obtain aliment for itself ; and its existence is pro- 

 bably a very brief one, being continued only so long as the store 

 of nutriment supplied by the egg remains unexhausted. In 

 Rotifer, however, as in by far the larger proportion of the class, 

 no males have been discovered ; and it remains doubtful whether 

 the two sexes are united in the same individual, or whether the 

 males are produced only at certain times. The female organ 

 consists but of a single ovarian sac, which frequently occupies a 

 large part of the cavity of the body, and which opens at its lower 

 end by a narrow orifice into the cloaca. Although the number 

 of eggs in these animals is so small, yet the rapidity with which 

 the whole process of their development and maturation is accom- 

 plished, renders the multiplication of the race very rapid. The 

 egg of the Hydatina is extruded from the cloaca within a few 



1 See Mr. Huxley's account of these organs, in his description of Lacinularia socialis, 

 " Transact of Microsc. Soc." Ser. 2, vol. i. Other observers have supposed that the 

 pyriform sacs communicate with the general cavity of the body; bnt the Author has 

 much confidence in the correctness of Mr. Huxley's statements on this point. 



