The Sexual Condìtions of Myzostoma glabrura (F. S. Leuckart). 307 



It may also be remarked that, liad von Grafp, whom we rightly 

 look upou as the chief authority on the group, felt bound to otfer 

 auy objections, he would probably bave done so in bis Challenger 

 Supplement (1887). 



From Wheeler's introductory Statements to bis ebapter on the 

 relations of the Myzostomidse to the Chictopod Annelids the reader 

 niigbt at first draw the inference, that the autbor was about to 

 assign the genus to a different positiou in the animai scale, whereas 

 in the sequel my former eonclusions are only confirmed and made 

 stronger by bim. Tbroughout bis work bis dissent from the results 

 of previous observers is insisted upon with such emphasis, and often 

 in such strong and unusual lauguage, that the more numerous oc- 

 casions, where be finds himself in a position to confimi this or that 

 previous discovery are apt to be lost sight of. But the points of 

 agreement are far more numerous than those of difference. 



Among other things an important advance would be, should it 

 turn out to be correct, Wheeler's attempi to identify the segmentai 

 sacs with lateral sense organs of the Capitellidaì. Unfortunately, 

 something more is wanting than the discovery of the passage of a 

 nerve to each of these structures. 



Glands are very often supplied by nerves, and, as it is probably 

 uunecessary to insist, the essence of a sense-organ is not founded 

 on the presence of a nerve alone, but also on the existence of a 

 group of sensory cells within the structure in question. None such 

 bave revealed themselves to Wheeler or to any other previous 

 observer, and bere, once more, it appears to me, that Nansen's view 

 had the facts on its side. 



Every worker, or almost every worker, undergoes the experience 

 of seeing some or other of bis results set aside by succeeding in- 

 vestigators. As Weismann once remarked, these latter should never 

 forget, that they stand, as it were, on their predecessors' Shoulders. 

 A dissertation is not infallible — even to its autbor — teu years 

 after it was written; and, wben the facts of a thesis come to be 

 revised by an experienced worker, with ali the newer methods and 

 the experiences of bis predecessors at bis disposai, and with an 

 extensive knowledge of how to set about the work, they as often 

 as not undergo considerable modification. 



And now, in connection with the facts recorded in preceding 

 pages, to inquire into Wheeler's eonclusions as to the hermaphro- 

 ditism of Myzostoma, or, to be more accurate, as to that of M. glahrum. 



20* 



