94 TAGE SK0GSBER6 



and N e s i d e i d s, a fact that I observed myself and that is l)v no means difficult to verify. 

 In this mode of crawling too it seems exjjedient for several pairs of legs to co-operate. 



The C y p r i d i n i d s pass their lives — provided they are not exclusively swimniin<; 

 or digging forms — partly in swimming about freely in layers of water just above the bottom, 

 partly in digging in the sand and mud of the bottom. ,,Zu einer eigentlich kriechenden Be- 

 wegung auf dem Grund sind die C y p r i d i n i d e n vermoge des Baues ihrer GliedmaaBen 

 durchaus unfahig; ich habe sie denn auch niemals in der Gefangenschaft sich in ahnlicher 

 Weise bewegen sehen." (G. W. Mulleh, 1894, p. 14.) In swimming and in digging the three 

 posterior limbs have no function to fulfil; swimming is carried out exclusively by the second 

 antenna, digging, as in the CytherelUdae, by a couple of the anterior limbs (the mandible, 

 sometimes the second antenna as well) and the furca. 



The H a 1 o c y p r i d s are exclusively pelagic forms ; they swim only with the second antenna. 



The P o 1 y c o p i d s cannot crawl. They either lie still on the bottom or take short 

 swimming trips to the layers of water just above the bottom. They swim with the first and second 

 antennae and the maxilla; as in the case of the H a 1 o c y p r i d s, the other limbs are not 

 used in locomotion. 



We thus find that the fifth and seventh limbs do not take part or take only a verv 

 slight part in locomotion in the case of freely swimming forms or in crawling forms in 

 which the crawling motions are helped by the more or less powerful upward and backward 

 natatory movements of the first antenna. In crawling forms whose first antenna does not 

 take part in locomotion the fifth and seventh limbs are developed as crawling legs. 



I do not mean by this, of course, that the method of locomotion was the only factor 

 that influenced the development of the two limbs just mentioned. Presumably, though not 

 certainly, other factors — botli internal and external — have, as G. ALM also supposes, 

 cooperated; among such presumable factors may be mentioned the nature of the sub-stratum 

 on which these animals live and presumably the nature of their food as well. In any case the 

 method of locomotion must be considered to have been an important factor. 



After this excursus I return to my discussion of G. \\. Muller's exposition of the organi- 

 zation of the P r o t o s t r a c o d s. 

 Vihrntoni piaics. J have nothing to add about his assumption as to the vibratory plates; it is not 



impossible that in this G. W. MOller has come very near to the truth, but it is by no 

 means proved. 

 '''"'•<" G. VV. MtJLLER assumes that the furca of the P r o t o s t r a c o d s was of about 



the same type as this organ in Conchoecia. This seems presumably to be a some premature 

 assumption. 



Comparatively short and powerful furcal lamellae, armed with several strong claws, 

 i. e. about the same type as in Conchoecia, is found in C y p r i d i n i d s, P o 1 y c o p i d s 

 and most of the Hal o c y p r i d s. In the other s t r a c o d s we find furcae of very varying 

 types. A number of forms, viz. C y t h e r i d s, have a very short and weak furca with a few 

 weak bristles. Others, viz. (' y p rids and N e s i d e i d s, are characterized by relatively 

 long and narrow furcal lamellae, armed with a comparatively small number of bristles and 



