G50 SYSTEMATIC HISTORY OF THE INFUSORIA. 



flame of a candle, and which most probably promotes the circulation of the 

 water contained in the canals. This water is apparently received from the 

 cloaca into the pulsating appendage, and from it transmitted to the various 

 parts of the tubular system, — a fact especially confirmed by Cohn's observa- 

 tions on Brachionus m'llitaris. Hence these water-vascular canals, with 

 theii' vibratile appendages, appear designed to convey streams of fresh water 

 to the interior of the animal, and thus, by exosmosis, aerate the fluid filling 

 the body of the animal, — the latter being continually driven to and fro during 

 the active muscular movements by which the creature alters its contour. 



The Rotatoria are provided with a reproductive apparatus, the female 

 organs being remarkably large and conspicuous (XXXVI. 4/). In the 

 majority of species the latter is the only portion that has hitherto been dis- 

 covered ; but in several, male organs have been found on separate indivi- 

 duals, indicating the bisexual nature of the class — at least demonstrating 

 the dioecious character of some of the species, a feature which will probably 

 be found to characterize the entire family. The ovary consists of a very thin 

 bag of structureless membrane (XXXVI. 4/), distended with clear fluid full 

 of granular molecules, amongst which are some cellular nuclei. The latter 

 successively attract around them portions of the granular fluid, thus forming 

 ova. In several species two distinct kinds of ova are produced by the same 

 individual, one being a true generative product, the other a modified ex- 

 ample of gemmiparous generation, and its growth independent of any sexual 

 process. The ovary communicates with the cloaca by means of a narrow but 

 dilatable oviduct. In examples of male animals that have been discovered, 

 there is a remarkable absence of all viscera, except the organs of reproduction 

 (XXXVI. 7, 8). "Whether all the Rotatoria are dioecious, or whether some 

 are hermaphrodite, the male organs having hitherto escaped detection, re- 

 mains to be ascertained. 



The bodies of the Rotatoria, unlike those of the Polygastric Infusoria, re- 

 tain a determinate form, never developing external gemmae, nor dividing by 

 spontaneous division. Even on emerging from the e^^, they possess all the 

 essential featuresof the matured animal(XXXVII. 16),neither passing thi'ough 

 a larval state nor being subject to metamorphosis like Crustaceans and Insects. 

 In the young animal some of the organs, especially the ciliated disks and 

 other external appendages, are imperfectly developed, but they imdergo httle 

 subsequent changes beyond an increase of size and definitivcness. Some 

 organs, as the red eye- spot, often disappear as the animal progresses to ma- 

 turity. The anterior extremities of the Rotatoria are furnished with various 

 arrangements of the disks or bulbs supporting niunerous cilia (XXXVI. 

 1 a and 4 a). These combine to form the rotatory organs, so designated from 

 the wheel-like aspect which they present when fully expanded and with the 

 cilia in motion. Though destitute of true articulated limbs, some species {e.g. of 

 Melicertci) have appendages not imlike the palpi of Crustaceans and Insects, and 

 which are probably tactile (XXXVI. 18 ; XXXVII. 17 d). Many fonns are 

 provided with a prolongation of the posterior part of the body, which is often 

 pointed (XXXVIII. 1), and with the articulations slipping into one another 

 like the joints of a telescope. This organ is sometimes furnished with a 

 terminal disk (XXXVII. 17 h), and is used like the tail of the leech, as an 

 organ of attachment. In other cases the disk is wanting, and its place sup- 

 plied by one or two digital appendages (XXXVI, 4 h), employed as anchors ; 

 whilst, in swimming, the entire organ appears to become a rudder, regulating 

 the direction in which the animal moves. 



The entire animal is invested by a thin peUucid membrane, which, from 

 its extreme tenuity and transparency, readily allows the examination of the 



