SCIENCE-GOSSIP. 



189 



STRUCTURAL FEATURES IN ROTIFERA. 



Bv Chas. F. Rousselet, F.R.M.S. 



T N reply to Dr. Stokes' recent notes on American 

 Rotifers, I hasten to inform him and other 

 readers of Science-Gossip abroad, that the curious 

 organ seen by him at the entrance of the oesophagus 

 into the stomach of Drachionus bakcri and other 

 rotifers, is also invariably present in the European 

 forms, and I cannot say why it is not mentioned in 

 Hudson and Gosse. In some species the oesopha- 

 gus seems to be prolonged as a little tube within 

 the stomach, an excellent arrangement to prevent 

 the return of the food particles, but the movement 

 of the tube is due entirely, I consider, to the action 

 of the flagelliform cilia, with which the inner wall 

 of the oesophagus is lined. These cilia are often very 

 long, and I have seen them individually in the oeso- 

 phagus of Asplanchna priodonta and A. brightwellii. 

 Again, with regard to the dorsal and lateral antennae, 

 they are almost universally present (in the Philo- 

 dinaea only the lateral antennae appear to be absent), 

 but sometimes very difficult to see. In Pterodina 

 the single dorsal antenna is always, the two lateral 

 antennae often, very small, but can always be found 

 with a sufficiently good glass, the latter high up near 

 the edge of the lorica nearly on a level with the jaws. 

 Mr. Gosse seems to have seen the antennae only in 

 a few of the larger species, and the reason for this 

 is obvious when the circumstances are considered. 

 Most of Mr, Gosse's work on rotifers was done in 

 the fifties and early sixties, when object-glasses 

 were much inferior to what they are now, and 

 later, in the eighties, when Mr. Gosse resumed his 

 work, he was past seventy years of age, and he 

 may well be excused if his eyesight was no longer 

 as good as in younger days. Further evidence on 

 this subject is furnished by the following passage in 

 his son's book, " The Life of P. H. Gosse," page 

 254: "Another and more permanent friendship 

 formed at Tenby (in 1854), was that with Mr. 

 Frederick Dyster, the zoologist, from whom he 

 bought, for ^^30, the microscope which he con- 

 tinued, regardless of modern improvements, to use 

 until near the end of his life." 



This old microscope is still in the possession of 

 his widow, and explains a good deal ; no one could 

 better describe and delineate what he saw than Mr. 

 Gosse, but naturally, his powers of seeing minute 

 details were limited by the quality of his microscope, 

 and the great wonder only is that he has seen so 

 much. 



The modern apochromatic lenses are so vastly 

 superior to the optical means at our disposal twenty 

 years ago, that we must not wonder at often finding 

 minute structures in rotifers, which our predecessors 

 in the study could not see, or could only imperfectly 



see under exceptionally favourable circumstances. 

 Thus, Mr. Gosse figures the tubules at the sides of 

 the body of Copeus pacliyurus, and says of them : 

 " I can discern, even with a high power, no setae 

 at the tips of these tubules." And yet they are 

 there, and readily seen with a modern apochromatic 

 J-inch. In many other rotifers I have found the 

 lateral antennae, although Mr. Gosse positively 

 states that there are none, because he could not 

 find any. 



I would earnestly advise students of rotifers not 

 to make new species, because of such minute 

 anatomical details, otherwise endless confusion will 

 follow. The descriptions and figures of the 

 rotifers we have are by no means quite accurate or 

 complete, and there is a great deal to be done in 

 checking and correcting the older observations, and 

 besides, a good deal of variation must be allowed 

 in the size and shape of some species. 



About 286 new species of rotifers have now been 

 named and described since 1889, when the Supple- 

 ment to Hudson and Gosse's Book was published. 

 A considerable number of these will have to be 

 struck off the list as being synonyms, or species 

 insufficiently figured and described. 



Dr. Stokes' new Salpina similis, described in the 

 " Annals and Magazine of Natural History " for 

 July last, is, it seems to me, identical with Gosse's 

 S. macracantha. His Notommata mirahilis is nothing 

 but our N . tyipus ; the two frontal and two lateral 

 antennae can be seen here as well as in America, 

 and the size and position of the tail varies some- 

 what. Further, it is certain, that even Gosse's N. 

 iripus and N.pilarius are one and the same animal; 

 the views of both figures can be obtained perfectly 

 by focussing higher and lower on the same animal. 

 The new Ratiuliis palpitatus is most probably 

 identical with Coelopns bvachiuvus. I am convinced 

 Mr. Gosse made a great mistake in founding the 

 genus Codopus, and describing the toes as one 

 within the other. His figures are fairly correct, 

 but his interpretation I consider wrong. All the 

 animals of this genus have two narrow, curved, 

 nearly equal toes, separated at the base, but joined 

 at the tip, thus leaving a clear space between and 

 moving together. This clear space Mr. Gosse took 

 for a toe lying in the hollow of the other toe. By 

 crushing a number of these animals the falacy is 

 quicky dispelled. 



I hope I have said enough to warn students of 

 rotifers against making new species simply because 

 they find some structure which is not mentioned in 

 the original description. 



27, Great Castle Strn-t. London, 11' 



