<" r.Vr.K SKOOSHKRC, 



and arinod with lumirruus Umj;. jinwcrtul nalatoiy bristk's; in .swiiiiiiiiug tliis limb stiiki-s powcr- 

 t'ullv upwards and backwards and soniowhat outward. The second antenna is a conibinod crawling 

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

 or at anv rate it does so only slightly. Tlic t'uiution of swimming is carried out In- the cudo- 

 podite. which is furnished with a cluster of long, pc)werful natatory bristles distally on the first 

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

 outward. Bv the combination of the ujjward and backward natatory movc^ments of tlie 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 in the I' o 1 \- c o p i d s. 

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

 but are furnished with long. |)ow('rful 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 (' v p r i d i n i d s, but its endopodite is better developed and is provided 

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

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

 assisted by the maxilla; this limb 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 methotl 

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

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

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

 ^^'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. MOller 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 have seen above, he assumed that the first antenna 

 of the Protostracods resembled that of the Cypridinids 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 have had the idea that 

 these animals swam about in the same way as the recent Cypridinids. 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 Protostracods. (Cf. also p. 67 above.) 



Did the Protostracods have any rostral incisur? G. W. 

 MtJLLER himself does not give any reasons at all for his assumption that they had. But this 

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



