seen in lln^ liilhl 

 oj llna pnnriplr. 



116 TAGE SKOGSBERG 



Is H. Woiirreck'^ This explanation given by R. WoLTERECK of the crest and spina in the D a p h n i d s 



explanniwn mrrn-i? ^^^ |.|^g anterior aiid posterior processes (the first antennae and the niucrones) in Bosmina as 

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



Even for the reasons put forward by this writer it seems to me 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 that these are among the most important. 



Wesenherg- Lund's Seen from this point of view the experiment with Bythotrefhes quoted on p. Ill 



experiment with By- above Carried out by C. Wesenberg-Lund seems more comprehensible. It seems surprising 



ihot replies seen J rnw removal of the fine spina should have so |)owerful an effect if it only influences the 



the point of fiew iij ^ J^ i • _ 



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

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



Chuns staiemeni Fresh light is also thrown upon the statement of C'. Chun quoted on p. Ill above with 



quoted on p. Ill petard to the connection between the force of the natatory movements and the direction of the 

 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. 

 What is the relation How docs the Ostracod group stand in relation to this problem? 



of the Ostrarods to ^w auswer to this question I must say that all the facts that I have ascertained during 



this pro em: ^^^^^ investigation of this group decidedly support R. Woi.terecK's view as given above. 

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



the Osirocods. 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 

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

 and very caleiforous 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. Gigantocypris, Thauniatocypris, even seem to be quite without lime. With regard 

 to the development of fat (oils) C. C^HUN* 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 C 1 a d o c e r e n, s t r a k o d e n etc. sind oft so iiber- 

 reich und so constant mit Oeltropfen ausgestattet, daC 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 — whicli 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 shell there is an exceedingly 



* The siiiiic wiitiM' :ils(i slates (loc. cit.) that „AusliiMunK v<'ii (iallerlsiibstan/. (lurch Aiifnahiiie von Wassor" 

 — as in, for inslaiiee, Ihe Hyperids — is also indiealed in some H a 1 o e y j) r i cl,s. As I havu not found any 

 other slalenieni of this soil in the literature nor ol)served anything similar in the rather abundant material investigated 

 by me. 1 must leave lliis inl'oi-nialion alone. « 



