THILODINAD.E. 103 



Goiius ROTIFER, Schrank. 



GEN. CH. Eyes two, ivithin the frontal column. 



At first sight it seems strange that so humble a form as that of Rotifer should 

 have succeeded, not only in attracting universal attention, but also in giving its name to 

 the whole class of animals to which it belongs. But there are good reasons for its hav- 

 ing done so. The genus is most widely distributed ; it has been found in almost every 

 quarter of the globe : apparently, indeed, wherever it has been looked for. It haunts 

 alike the damp moss on the Great Sidelhorn at a height of 8,000 feet, and the swamps 

 and sea-weeds of the Finnish coast ; and seems equally at home under the ice in moor- 

 pools on St. Gotthard, and in the irrigating ditches of the gardens at Cairo. It is, too, 

 as prolific as it is common, and breeds in captivity as freely as when at liberty. More- 

 over, the genus Botifcr exhibits the wonder of ciliary rotation in its most effective form ; 

 for its ■m.-eath when in full action looks precisely like a pair of escapement-wheels of a 

 watch, whirling round at great speed, the cogs looking " sometimes like the ancient 

 battlements of a round tower ; at others ending in sharp points, and forming a kind of 

 Gothic crown ; now bent all the same way like so many hooks, and now with their ends 

 clubbed like a number of little mallets." How a living creature could possess or use 

 such a contrivance was a hopeless riddle to the early observers ; though even some of 

 the earliest expressed the opinion that the appearance was an optical illusion. 



But the marvels of tlie genus did not end here. It had been asserted by Leuwenlioek 

 that the creatiures might be dried up for months, and yet be restored to life again. This 

 was enough to fire the dullest imagination ; and as also a brisk controversy sprang up 

 about the accuracy of this assertion, the charms of a dispute were added to those of a 

 JRotifer, and it was no wonder that the genus secured all its honours ; and, like the 

 bramble, was raised by circumstances to a position which it little deserved. 



The whole structure of the genus is so nearly that of Philodina, that it requires but 

 little notice. The eyes are placed close together within the column, generally near the 

 extremity, instead of in the neck, as in the case of Philodina. Nerve-threads have been 

 traced to them and light-refracting bodies seen in them, in the case of Botifcr vulgaris, 

 by Dr. Zacharias. The only portion of the internal organization that has not been satis- 

 factorily made out is the reproductive system. Just as in Philodina, no oviduct has as 

 yet been discovered ; and no one has explained how it is that the living young pass from 

 their apparently free position in the body-cavity into the cloaca, through which they 

 have been seen to issue.' 



The male, too, is equally unknown ; a strange fact, when one considers first that the 

 structure of the female reproductive organs, so far as it has been studied, is that of a 

 typical Eotiferon ; and secondly, that thousands of specimens of this genus must have 

 been watched by many practised observers, during the century and a half which have 

 elapsed since the animals were discovered. 



' It is possible that the long thread, which is often seen to jiass from the posterior end of the ovary 

 towards the cloaca, may really be, not a muscle, as is usually sujipos-'J, but the collapsed oviduct ter- 

 minating in the cloaca. Should this be the ease, then the ovum, when it drops from the ovary, does 

 not fall into the body-cavity, as has been supposed, but simply stretches out over itself that portion of 

 the delicate investing membrane, which had up to that moment been shrivelled into a mere cord. 

 As the membrane investing the ovary is of extreme tenuity, it is just possible that it has escaped 

 observation when extended, not only over the ovary, but even over the developed young. If this expla- 

 nation prove correct, there is nothing abnormal in the reproductive system of Rotifer. Mr. Gosse quite 

 concurs with me in taking this view of the case : a view which had occurred to him before he read 

 my note. 



