studies on marine Ostracods 69 



this author points to the reduced vibratory plates on the posterior hmbs in Nesideidae and the 

 conditions in the Cytherellids. 



The brush-shaped organ is considered by this writer to be homologous with iin,xh-^i,ni,rd organ 

 an eighth limb. This limb would have been found in both males and females of the P r o t- 

 ostracods and have belonged to the segment behind that of the seventh limb. The ])Osition 

 of this organ near or just behind the fifth limb is considered to be a secondary one. 



The f u r c a of the Protostracods would have been of about the same type Furcn. 



as this organ in Conchoecia. 



This author does not express any opinion about the sexual organs. sexuui organs. 



In this cormection he does not mention the rod-shaped organ either. It is Hodshniied urgan. 

 merely stated on p. 161 that this organ is „lediglich" homologous in C y p r i d i n i d s and 

 Halocyprids. 



Although this view of the Ufe, organization and the development of the Prot- a criticism of a. w 

 ostracods, as worked out by G. W. MOller, is very meritorious, it is, nevertheless, ■^^"'''^'■'*' ''"•'"' "f ''" 



....-., ' Protostracods. 



open to criticism m many details. 



According to this author tlie Protostracods swam freely. H o w d i d ^'^"«' '^''^ ''«« P^ot- 



,1 • Q ostracods move? 



they s w 1 m? 



We can distinguish three types of swimming in the recent Ostracods; first the 

 method of swimming found among C y p r i d i n i d s and most H a 1 o c y jj r i d s, secondly 

 the method of swimming in the Gyp rids and P o 1 y c o p i d s, and thirdly that found in the 

 genus TJiaumatocypris. The Cypridinids and most of the Halocyprids use what one 

 might call rostral incisur swimming. They do not use the first antenna as a natatory organ, 

 a fact that was pointed out by G. W. Muller in 1894, p. 23: ,,irgend welchen Antheil an der 

 Schwimmbewegung nimmt hier die 1. Antenne siclier nicht.'" I have also been convinced of 

 the correctness of this observation by examination of living animals. It is to be noticed, in 

 addition, that the structure of this antenna makes it anything but suitable for a natatory organ. 

 Thus G. W. MfJLLER writes, 1894, p. 24: ,,Auch ihr Bau macht mir eine Mitwirkung daran 

 wenig wahrscheinlich."* On the other hand the second antenna, which is the only natatory 

 organ of these forms, is particularly well suited by its organization to fulfil this function. It 

 is very powerful, its protopodite is very large and full of powerful muscles which move the 

 exopodite. This is long and cylindrical and is fitted with long, powerful natatory bristles and 

 joined very loosely to the protopodite. Each valve in these forms is furnished anteriorly with 

 an incisur, the rostral incisur, and in swimming the exopodite rests with its basal joint in this 

 almost as an oar rests in a rowlock.** In swimming the exopodite moves almost straight out 

 at the sides and backwards, only slightly downwards; in this way a straight forward motion 

 of the animal is produced. The endopodite of this limb is more or less reduced in these forms 

 and does not play any part in swimming. In the C y p r i d s that have no rostral incisur both 

 the first and the second antenna take part in swimming. The first antenna is long, cylindrical 



• G. S. iJRADY ;uul A. M. XoRMAN assumc, however, 1896, ]>. &la. that this limb is used in swininiin^r. 

 ** Of course I do not mean l>y this lliat the arlion in lliis kiml nf s\vin\ininfr is th>' saini' as in rowing. On l\v 

 contrary this is not at all the case. 



