116 TAOR SKOOSBKRO 



> li. Wultfreikg Tliis oxphinatiim givou by K. \\ (.)l.Ti;i;i:i;K of tlic crost ami spina in the I) a j) h ii i d s 



planaiion correct^ j^^^^j j|^^^, aiitorior and posterior j^roccsses (the first antennae and the niucrones) in Bosmina as 

 steering and stability organs is certainly very interesting, but is it correct? 



Even for the reasons put forward l)y this writer it seems to nie very probable that 

 this question must be answered in the affirmative. We may grant that they do not posses these 

 functions alone, but it seems certain tliat these are among the most important. 

 Vfienhfrs-Lunds Seen from this point of view the experiment witli Bythotrephes quoted on p. Ill 



prrmrnt uuh By- above Carried out by C. Wesenberg-Lund seems more comprehensible. It seems surprising 

 e point of t'iea- of t^** t^^ removal of the fine spina sliould have so powerful an effect if it only influences the 

 Wniiereck's position of equilibrium. If, on the other hand, the function of this process as a steering and 

 prmcip e. stability organ is taken into consideration, we have a different state of affairs. 



Chun's statement Fresli liglit is also thrown upon the statement of C. Chun quoted on p. Ill above with 



quoted on p. Ill j^gard to the connection between the force of the natatory movements and the direction of the 

 of this principle, processes. No causal Connection seems to exist between these two factors; on the other hand the 

 direction of the processes is presumably dependant on the direction of the natatory movements. 

 <rhat is the relation How does the Ostracod group stand in relation to this problem? 



I the Ostracods to j^ answer to this question I must say that all the facts that I have ascertained during 



my investigation of this group decidedly support R. WolterecK's view as given above. 

 The ovenveight of In all the planktonic forms of this group, as in the Cladocera, a decrease of the over- 



the Ostracods. weight Can be established. This decrease is often brought about by a reduction of the amount 

 of lime in the shell, by the chitin and a large number of tissues becoming finer and by the 

 development of fat. We find a good example of the reduction of the lime in the genus 

 PhUomedes; while during life at the bottom the species of this genus are characterized by heavy 

 and very calciferous shells, during the pelagian period, i. e. the time just after the moult at 

 which maturity is reached, they have shells comparatively poor in lime. A number of pelagian 

 forms, e. g. G-igantocypris, Thaumatocypris, even seem to be quite without lime. With regard 

 to the development of fat (oils) C. Chun* wrote as early as 1896, p. 101: ,,Weit verbreitet 

 ist hingegen das Auftreten von Oeltropfen, welche durch ihr geringes specifisches Gewicht 

 das Schweben ermoglichen. Die Cladoceren, Ostrakoden etc. sind oft so iiber- 

 reich und so constant mit Oeltropfen ausgestattet, daB gerade den mit relativ glatten Ober- 

 flachen versehenen Organismen das Schweben ermoglicht wird." — In a few cases (the 

 species of the genus Gigantocypris) the decrease of the specific gravity has gone so far that 

 we may speak of passive buoyancy. In this genus — which lives both at very great depths 

 (2700 — 3600 metres) and near the surface of the ocean (about 200 — 150 metres in the Sargasso 

 sea, consequently in water of comparatively slight viscosity) — the specific gravity seems 

 practically to correspond to that of the surrounding medium; the tissues are fine and 

 exceedingly aqueous; when one dissects the animal from the sheU there is an exceedingly 



* The same WTiter also states (loc. cit.) that ,,Ausbildung von Gallertsiibstanz durch Aufnahme von Wasser" 

 — as in, for instance, the Hyperids — is also indicated in some H a 1 o c y p r i d,s. As I have not found any 

 other .-statement of this sort in the literature nor observed anything similar in the rather abundant material investigated 

 bv me. I must leave this information alone. 



