Sliulii'S on marine^ Oslracods 36 1 



Bygning som hos de 2 foregaaende Slaegter; men de er forholdsvis mindre kraftigt udviklede, 



og de til Sv0mmegrenen faestede Barster er ualmindelig korte, med Cilieringen grovere og 



mindre taet. I Yirkeligheden kan disse Lemmer hos Hunnen kun uegentlig kaldes Svamme- 



antenner, da de ikke benyttes til Svomning, men kun som et Slags Arme .... ved Dyrets 



langsomme krybende Vevaegelser paa Havbunden."'* The drawing with which G. O. Sars 



illustrates this description shows an antenna of about the same structure as the larval one. 



i. e. with relatively short, unbroken bristles, well pointed distally, on the exopodite; curiously 



enough in this drawing all the bristles of the exopodite have natatory hairs. From this 



description and figure it seemed to me probable that the peculiarity of breaking-off the 



natatory bristles would also be a characteristic of this species. In order to be absolutely 



certain on this point I wrote to Professors fr. O. Sars and G. S. BRADY asking for permission 



to investigate their specimens. Both these investigators were kind enough to send me several » 



specimens. Among the specimens sent by Professor Sars there was only one (probably) mature 



female; this specimen unfortunately, however, was represented only by two emptv valves. 



Among Professor Brady's specimens there was a complete female with verv large eggs in the 



brood chamber. Contrary to G. O. Sars's statement this specimen had, on the e.xopodite of 



the second antenna, like Ph. ( Sderoconcha) Afpellofi, relatively short and quite bare bristles 



on the second to the fourth joints; the bristles on the following joints were long natatory 



bristles of the same type as in the female of Ph. (Ph.) globosa during its pelagian stage. 



What is the connection between these facts and the view put forward by 6. W. MttLLER, 

 1908, that the peculiarity of breaking off the natatory bristles in the genus Philomedes is not 

 a ])lienc)menon of convergence, but that it is to be referred to a conmion inheritance? 



It is obviously difficult to fit them in with this theory. Philomedes ( Sderoconcha) Appello/i The brcakinn of/ ../ 

 and Ph. (Ph.) rotunda represent two tvpes rather strongly differentiated from Ph. (Ph.) qlobosa '''" ""'<"'•':» ''nstl^'s 



*.,.".. o phenomenon if 



and Ph. (Ph.) assimilis; the first-mentioned species especially differs comparativelv greatlv ronoergenr,-? 

 from the otliers. lu all tliese ioui forms the natatory bristles are broken off. In Ph. (Ph.) 

 Eugeniae, which is certainly very closely related to Ph. (Ph.) globosa and Ph. (Ph.) assimilis. 

 and in Ph. (Scl.) Folini, which is very closely related to Ph. (Scl.) Afpellofi the natatory bristles 

 remain unbroken throughout the whole life. 



Contrary to G. W. MCller's view, it seems to me necessary to assume that the peculiar 

 character of breaking off the natatory bristles of the exopodite of the second antenna in the 

 genus Philomedes is not the result of common inheritance but of convergence. 



It is of course impossible at the present time to give any certain causes for this pheno- 

 menon. Tiie following facts are, however, striking: 



1) All the species (five) of this genus from warm or temperate seas tliat were in- 

 vestigated with regard to this character proved to have long, unbroken natator}- bristles 

 during the whole year. 



* The siHornl pair of anlonnai' in llic finnale ccrlainiy show, on thi' wlioii'. the samo slrin'luri' as in the- two 

 pi-wedinK jjonera; l)nl flicy are I'omparalively less powerfully (levelopeii. anil Ihi' bristles that are attaelieiJ to Ihi' 

 natatory branch are unusually short, with their hairs roarser and situated less densely. As a matter of faet these 

 limbs in the I'eniale eannol really be called swiminitif,' antennae, as they are not used for swimminjr, hut only as a sort 



of arms .... in the animal's slow clawlins movements al the bottom of the sea. 



