122 PROF. A. DENDY AND MR. E. HINDLE : ADDITIONS TO 



individuals than in others and also that they have no definite arrangement, 

 but are scattered haphazard over the peritoneal epithelium. In RhahdomoJgus 

 ruber these organs appear to be absent *, a fact which also supports our 

 sug-gestion as to their nature. 



A variety o£ functions have been assigned to these organs, but none of 

 them seem very probable. Some authors have regarded them as excretory 

 organs ; others suppose that they serve to maintain the circulation of coelomic 

 fluid ; whilst one regards them as accessory respiratory organs. Semon f 

 described those of Synapta in detail, and came to the conclusion that they are 

 " lymph-stomata.''^ Ludwig discusses the question and also gives references 

 to the literature in his work on the " Holothuroidea" in Bronn's ' Klassen 

 und Ordnungen des Thier-reichs.' Although differing considerably in 

 structure, the ciliated urns of the Sipunculidse may perhaps be cited as a 

 parallel case of structures previously regarded as integral parts of the animal 

 in which they occur and subsequently as parasites. 



The genus Rliahdomolgus was founded by Keferstein in 1863 for an appa- 

 rently pelagic Holothurian observed only once, at St. Vaast, and to which he 

 gave the specific name ridwr % . Ludwig has recently re-described the species 

 after an interval of forty-two years {loc. cit.). 



That the New Zealand species is distinct from that found at St. Yaast can, 

 we think, scarcely be doubted. In the latter the tentacles are " undivided, 

 slightly lobate on the sides," whereas in our species the pinnse of the tentacles 

 are well developed. An even more striking difference is the enormous size 

 of the New Zealand species as compared with the European one. 



The probable relationship of Rhabdomolgus to Chirodota is discussed under 

 the heading of Chirodota geminifera, sp. n. 



EXPLANATION OF THE PLATES. 



Plate 11. 



Figs. 1-4. Rhabdomolgus novcs-zealandice, sp. n. 



Fig. 1. Sketch of the entire animal, (x 2.) 



Fig. 2. Transverse section of an otocyst. (X 550.) 



c.e. = cubic epithelium ; d. = thin part of wall ; n. = nerve supplying otocyst : 

 ot. = otoliths. 



* Ludwig, " Ein wiedergefundenes Tier: Rhabdomolgus rMier, Keferstein/' Zoologischer 

 Anzeiger, Bd. xxviii. (1905) pp. 458-459. 



t Semon, Beitrage zur Naturgeschichte der Synaptidendes Mittelmeeres. 2. Mittheilung. 

 Mittheilungen aus der Zoologischen Station zu Neapel, Bd. vii. p. 416, Taf. 15. figs. 9-15. 



X Keferstein, " Untersuchungen iiber niedere Seethiere," Zeitscbrift fiir wissenschaftliche 

 Zoologie, Band xii, pp. 34-35, Taf. 11. fig. 30. 



