92 TAGE SKOGSBERG 



for these families to be taken into consideration in this connection. See also the remark 

 above, p. 89. 



From what has been shown above it seems to follow that G. Alm's assumption that 

 the seventh limb was developed as a cleaning organ in the cases where the mastication 

 had been intensified by the development of the fifth limb as a masticatory organ cannot 

 be maintained. Nor have I succeeded in establishing any condition of correlation between 

 the development of the masticatory parts of the mandible and maxilla on the one hand and 

 the seventh limb on the other. 



Does there not exist, however, a certain correlation between the fifth and seventh 

 limbs? Or, as I should prefer to put the question: ^^^ich factor or factors have exerted an 

 influence in the development of these appendages? WTiat is more natural in dealing with this 

 problem than first to try to discover whether this development has not been connected with the 

 method of locomotion of these animals? 



Let us once more take the case of the family Cypridae first. If one observes a (Jypris 

 in motion on the bottom one can easily discover that with the help of the first antennae, which 

 strike regidarly upwards and backwards, and the second antennae, which either strike down- 

 wards and backwards or carry out crawling movements, it seems rather to glide than to crawl 

 heavily over the sub-stratimi. Owing to the natatory movements of the first and second antennae 

 the representatives of this genus natm-ally have less need of effective assistance from the poste- 

 rior limbs for locomotion. This applies, of com'se, still more strongly to the powerful swimmers 

 in this family, e. g. the genera Cypria and Cydocypris. The same method of locomotion as in 

 the genus Cypris is found in a nmnber of representatives of this family; I need only mention 

 here as examples the genera Pontocypris, Erythrocypris and Iliocypris. G. W. MUller writes 

 about the representatives of the sub-family Iliocyprinae in ,,D e u t s c h 1 a n d s S ii B w a s s e r- 

 s t r a c o d e n" 1900, p. 90, that besides freely swimming they generally ,,sich rasch g 1 e i- 

 t e n d iiber den Grund bewegen". There are, however, representatives of Cypridae that are 

 unable to swim at all; I need only mention here as examples the genera Candona and Macrocypris , 

 as well as the females and partly the males too of the genus Argilloecia. But this does not exert 

 very much influence on what might be called the principle of crawling, as these forms also have 

 rather long, stiff bristles on the first antenna — though not so long as in the swimming species. These 

 forms use the second antenna and the sixth limb in crawling. This movement would, however, be 

 very heavy and uncertain unless in these genera too the first antenna struck upwards and backwards 

 in the same way as in the swimming forms and so help very much both in keeping the aninutl 

 in equilibrium and in propelling it forward. Thus in all the forms belonging to the family 

 Cypridae the first antenna is used in crawling in a way that gives both comparatively great 

 rapidity and also good stability to the uKJvement. 



The mode of life of the family Darwinulidae is too little known for us to use it in this 

 argmnent. It has presumably about the same method of locomotion as the N e s i d e i d s and 

 Cytherids, so that I shall only refer here to what is said in connection with these families. 



The family Cytlierellidae is also very little known oecologically; they are slow, digging 

 forms without any power of swimming. The digging life luis to a great extent left its impression 



