71) " TAOE SKOGSBERa 



and armed with numerous long, powerful natatory bristles; in swimming this limb strikes power- 

 fully upwards and backwards and somewhat outward. The second antenna is a combined crawling 

 and swimming organ. Its exopodite is reduced and does not seem to take part in swimming, 

 or at any rate it does so only slightly. The function of swimming is carried out by the endo- 

 podite, which is furnislied with a cluster of long, powerful natatory bristles distally on the first 

 joint. In swimming this limb is moved powerfully downwards and backwards and somewhat 

 outward. By the combination of the upward and l^ackward natatory movements of the first 

 antenna and the downward and backward movements of the second antenna the animal is 

 propelled straight forward. The same principle of swimming is found !n the P o 1 y c o ]) i d s. 

 These forms also liave no rostral incisur. Their first antennae are certainly rather short, 

 l)ut are furnished with long, powerfid natatory bristles and in swimming strike upward 

 and backward, somewhat outward. The second antenna is of about the same type as this 

 appendage in the C y p r i d i n i d s, but its endopodite is better developed and is provided 

 with long, powerful bristles. In swimming both the exo- and the endopodite are used; they 

 both strike powerfully downward and backward and somewhat outward. In this they are 

 assisted by the maxilla; this liml^ is provided with long and rather powerful bristles both at 

 the end of the exo- and the endopodite and, like the second antenna, it strikes powerfully down- 

 ward and backward in swimming. In Thaumatocypris too, in which we find the third method 

 of swimming, there is no rostral incisur. This genus has a first antenna of about the same type 

 as is found in the y p r i d s and a second antenna of about the same type as that of tlie 

 P o 1 y c o p i d s. In swimming both the first and the second antenna strike downward and 

 backward (and probably somewhat outward). Such a method of swimming would obviously 

 cause tlie animal to have a rotatory motion if there were not special means for preventing this. 

 V\'e have such means, however, in the long spines that issue from the shell (cf. the chapter on 

 the adaptations for planktonic life in this treatise). 



Did the Protostracods use any of these three methods of swimming? 



G. W. MUller himself does not give any direct information with regard to this. From 

 some statements in his monograph of 1894 we can, however, indirectly get an idea of this 

 writer's opinion on this subject. As we liave seen above, he assumed that the first antenna 

 of the Protostracods resembled that of the C y p r i d i n i d s most closely. As 

 in another part of this work he has pointed out that this antenna, on account of its structure, 

 is not suitable as a natatory organ and has himself discovered that it is not used as such, he 

 could not have been of the opinion that this appendage took part in the operation of swimming in 

 the Protostracods. He thus seems presumably to have meant that in the latter 

 only the second antenna acted as a natatory organ, i. e. he seems to ha\-e had the idea that 

 these animals swam about in the same way as the recent C y p r i d i n i d s. That this was 

 really his opinion is also shown by the fact that he assumed the rostral incisur to be a character 

 belonging to the P r o t o s t r a c o d s. (Cf. also p. 67 above.) 



Did t h <• P r o t o s t i- a c o d s h a v e any r o s t i- a 1 i ii c i s u r? G. \V. 

 MtiLLER himself does not give any reasons at all for tiis assumption that tlie\- had. But this 

 assumption needs to be proved in iikuc detail even perhaps more than most of the others. 



