studies nil marine Ostrarods 561 



Some limbs are eijuipped with specific sens o r y 1) r i s 1 1 e s. 



There are never any traces of gills. 



The mother does not take care of the eggs after these are laid. The only exception 

 to this rule so far known is the species Euconchoecia Chierchiae, dealt with by m(> in this work, 

 in which the eggs are kept for a time between the back of the body and the shell of the female, 

 as in the sub-order Cypridinifnrines. I have not been able to observe any development of organs 

 in the eggs that occur in the brood chamber of the species mentioned. 



Habitat: — The forms are marine, all, as far as is known, holoplanktonic. 



Historical: — While a rather large number of investigators, both early and mcxlern, 

 have contributed to the study of the morphology and classification of the Cypridiniformes, 

 the Halocyprids, on the other hand, have been dealt with in detail by only a few writers. 

 Because of this the history of the investigation of the latter group is considerably simpler than 

 that of the former. 



I should liki' to bring forward tiie following arguments against this explanation: 1) The organ has no pigment 

 or other characteristics that are found in organs which are explained as visual organs. 2) It is impossible to establish 

 any relation between the development <if this organ and the strength of the light. The Halo c y p r i d s comprise 

 forms that live near the surface of the sea as well as those that live at very great depths (G. W. Mlller states, for 

 instance, 1906 a, that a number of specimens were caught by the „Val d i v i a" with a closing net at depths of from 

 :i',iO() — 2700 metres), and yet there is not the slightest indication thai the great variation in this organ is in any way 

 influenced by the strength of the hght. 3) \o relation seems to exist between the development of the rod-shaped organ 

 and that of the median and lateral eyes, as is shown by the following examples. The Halocyprids, which have, as we 

 know, in most I'ases an exceedingly well-developed rod-shaped organ, are quite without median and lateral eyes. In the 

 sul)-genus Vargula (I assume here that the rod-shaped organ has the same function in Halnci/prifornics and Cypridini- 

 formes, an assumption which is made, however, with the greatest reservation; cf. [). 96 above), whose rod-shaped 

 organ is short and thick and comparatively well developed, the lateral eyes are generally large. In such forms as have 

 more or less completely reduced lateral eyes no reduction or increase can be established in the rod-shaped organ: examples 

 of this are shown in the closely related species Cypridina (V.) antarclica and C. (V.) nori'egica. In the Macrocypridina 

 the lateral eyes are large, the rod-shaped organ is small. In C'rossophnnis africanus both the lateral eyes and the rod-shaped 

 organ are reduced; cf. G. VV. Muller, 1906 a, p. 135. Philomedes perhaps affords the best example. In this genus 

 the rod-shaped organ is particularly well developed and has about the same type and relative size both in mature males 

 and females and in larvae (it is probably developed even in the earliest postembryonal stages). The lateral eyes arc, 

 on the other hand, as we know, subject to very great variations in these forms. The females are quite or [)ractically 

 quite without lateral eyes both as larvae and matun^ specimens. Tlu- mah^ larvae have lateral eyes, although these are 

 rather small and comparatively slightly pigmented. The mature males of this genus are, on the other hand, as we 

 know, furnished with large, well pigmented lateral eyes. Other examples from this sub-order could equally well 

 have been chosen, the result would have been the same, quite negative. 4) Another argument against G. W. Muller's 

 explanation is probably to be fo\ind in the position of the rod-shaped organ in relation to the light-producing glands 

 i n Cypridin i formes. 



II o w a r e w t^ I h e n to ex p lain I h e v o d - s h a j) e d o r g a n? 



C. Glaus has interpreted it as ,,Tragt;r eines ausgepriigten Tast ■ und Spiirsinnes" (1891 a, p. 35). G. W. Muller 

 reji-cts this explanation in his work of 1 894 ; this WTiter's proofs and ciunilcrproof s in this problem seem to me, however, 

 anything but decisive. Perhaps we are obliged to say that it is an organ whose function we do not yet know. Perhaps 

 we can — mutatis mutandis — apply in this case a statement of A. Sedgwick's ( \ Student's Textbook of Zoology, 1909, 

 vol. III. p. 637): ,,It is more tluiii probable that insects have sense organs which have no counterparts amongst verte- 

 brate animals and these we cannot even hope to invi^stigale". — I have myself carried out a largo number of experi- 

 ments on this organ at the Russian Zoological Station at Villefranche-sur-mer and at the Musee Oceanographique of 

 Monaco and I hope to present the results of these in a later |iuliliia1ioii. 



Zoolog. bi(Jr.aR, Uppsala. Siippl.-Bd. J. ? 4 



