Sludit's on inariiie Ostracocis 561 



Some limbs are equipped with specific sens o r y b r i s t 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 me 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 Cypridiniformes. 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 modern, 

 have contributed to the study of the morphology and classification of the Cypridtni/urmes, 

 the H a 1 o c y p r i d s, 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 likr lo liiiiig I'oiwaiil llic lollipwiiig aiguiiKMils agiiiiisl Uiis uxplaiialidii: 1) Tlif organ has no ((ignionl 

 or other characterislics that are found in organs wliich are explained as visual organs. 2) 11 is impossible lo establish 

 any relation between the development of this organ and the strength of the light. The H a 1 o c y p r i d s comprise 

 forms that live near the surfaee of the sea as well as those that live at very great depths (G. W. .Mi llf.r slates, for 

 instance, 1906 a, that a number of specimens were caught by the .,^■al di vi a" with a closing net at depths of from 

 3300 — 2700 metres), and yet there is not the slightest indiiation that the great variation in this organ is in any way 

 influenced by the strength of tlie light. 3) No relation seems lo 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 H aloey prid s. which have, as we 

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

 snb-genus Vargida (I assume here that the rod-shaped organ has the same function in II nlnci^pri formes and Ci/pridini- 

 jormcs, an assumption which is made, however, witii the greatest reservation; cf. p. 96 above), whose rod-shaped 

 organ is short and thicli 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.) anlarcUca and C. (V.) norvegica. In the Macrocypridina 

 tlie lateral eyes are large, the rod-shaped organ is small. In Crossophorus africanus both the lateral eyes and the rod-shaped 

 organ are reduced; cf. G. W. Mijller, 1906a, p. 135. Pliilomedca 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 are, 

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

 quite without lateral eyes both as larvae and mature si)ecimens. The male larvae have lateral eyes, although these are 

 ratlier small and wjmpani lively slightly pigmented. The mature males of this genus are, on Ihe other hand, as we 

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

 have been chosen, the result would have been the same, quite negative, 'i) .Vnother argument against G. W. .Mi llkiis 

 explanation is probably lo be found in the position of the rod-shaped organ in relation lo the light-producing glands 

 in Cypridiniformes. 



H o w a r e w <; I li e n t o e x p 1 a i n t h e r o d - s h a p e d o r g ;i n? 



C. Glaus has interpreted it as „Tragcr cines ausgepraglen Tasl • und Spursinnes" ( 1891 a. p. 35). G. W. Mi llkh 

 rejects lliis explanation in his work of 1894 ; this writer's proofs and counterproofs in this problem seem In me. however, 

 anything but decisive. Perha|)s we are obliged to say that it Is iin organ whose function wi' do not yet know. Pi'rhaps 

 we can — mutatis mutandis — apply in this case a statement of .\. Skug wick's (.\ Student 's Tcxtbnok of /.niilngy, 1909, 

 vol. Ill, p. 637): „ll is more than probable that insects have sense organs which have no counlerparls amongst verte- 

 brate animals and these we cannot even hope to investigate". — I have myself carried out a large iiunil>er of experi- 

 ments on this organ at the Russian Zoological Slalion at X'illefranilie-sur-mer anil ;il llu' ■\Iusee Oceanogniphique of 

 Monaco and 1 ho|ie lo present the results of these in a later publication, 



1 1 



Zoolog. biirair, Uppsala. Suppl.-Bd. I. ■ ' 



