EEPEODUCTIVE OEGANS. 445 



delicate." The opinions of the Professor himself concerning the nature 

 of the organs which he describes being so indefinite, we must pause 

 before adopting the physiological views to which their admission would 

 lead more especially as, from the very fact of the whole visceral cavity 

 being perpetually filled with aerated fluid, the existence of any localized 

 organs of respiration could hardly be esteemed necessary. 



(1152.) The two lateral bands above mentioned (fig. 225, T), with 

 which are connected the " trembling gill-like organs" of Ehrenberg, are 

 now considered as constituting a peculiar apparatus, distinguished as 

 the " water-vascular system," of which, as they exist in Lacinularia 

 socialis, the following description is given by Professor Huxley*. In 

 this species there is no contractile sac as in other genera ; but two very 

 delicate vessels, about 4 ^ O th of an inch in diameter, clear and colour- 

 less, arise by a common origin upon the dorsal side of the intestine. 

 The vessels separate, and one runs up on each side of the body in the 

 direction of the mouth. Arrived at the level of the pharyngeal bulb, 

 each vessel divides into three branches : one passes over the pharynx 

 and in front of the pharyngeal bulb, and unites with its fellow of the 

 opposite side ; while the other two pass, one inwards and the other 

 outwards, in the space between the two layers of the trochal disk, and 

 there terminate as ca3ca. Besides these, there seemed sometimes to be 

 another branch just below the pancreatic sacs. 



(1153.) A vibratile body is contained in each of the caBcal branches, 

 and there is likewise one on each side in the transverse connecting 

 branch. Two more are contained in each lateral main trunk, one oppo- 

 site the pancreatic sacs, and one lower down, making in all five on each 

 side. Each of these vibrating bodies is a long cilium ( T ^ nr th of an 

 inch), attached by one extremity to the side of the vessel, and by the 

 other vibrating with a quick undulatory motion in its cavity, giving rise, 

 as Siebold remarks, to an appearance singularly like that of a flickering 

 flame. 



(1154.) The last subject that we have to consider relative to the 

 internal economy of the Rotifera is the conformation of their generative 

 apparatus, which here assumes a considerable perfection of development. 

 The reproductive system is composed apparently of two distinct parts ; 

 the one subservient to the formation of the ova, the other destined 

 either to furnish some secretion essential to the completion of the egg, 

 or, as has been surmised, secreting a fertilizing fluid by which the 

 impregnation of the ova is effected prior to their escape from the body. 



(1155.) In Melicerta ringens, as we learn from Professor William- 

 son's admirable memoir, the ovary is a hollow sac, consisting of a very 

 thin pellucid membrane, filled with a viscid granular protoplasm of a 

 light-grey colour, in which may be perceived some twenty or thirty 

 nuclei, each containing a nucleolus in its interior; these seem to be 

 * Quarterly Journal of Microscopical Science, no. 1. p. 6. 



