74 TAGE SKOGSBERG 



Thus the fourth post-oral limb, or according to the terminology used in the present 

 work, the sixth limb, of this species belongs, according to G. W. MUller , to the segment represen- 

 ted by the second chitinous stripe. No reasons are given for this statement; we are obviously 

 concerned with a purely external position. If we turn to the figure to which G. W. MtLLER 

 refer, we find a certain difficulty in finding the orientation of the limb mentioned in 

 relation to the chitinous stripes; as G. W. MULLER himself points out, the latter are not 

 directly connected with the bmbs, as is the case in the C y t h e r i d s. It seems to me to be 

 most closely connected with the most anterior of the chitinous stripes drawn in the figure. If 

 we start from this orientation we shall find nine more , .segments" come after this ,, segment", 

 i. e. the number given by G. W. MULLER himself. (The most anterior chitinous stripe in this 

 figure would thus represent the second ,, segment", the most anterior one not being drawn). 

 If we compare with this pi. 32, fig. 5, which represents the back of the body of the male Cytherella 

 sordida, we find the following facts. The orientation of the sixth limb is, if possible, more 

 difficult than in the figure of the female. It seems to be most closely connected with the next 

 to the most anterior chitinous stripe. If we start from this orientation, only five more ,, segments" 

 would come after the ,, second segment", i. e. four less than the number given by G. W. MOLLER; 

 if we assume that this limb belonged to the anterior chitinous stripe, the number of ,, segments" 

 that follow would be three less than the number given by this author. In the male the number 

 of the chitinous stripes at the back of the body is, at least if we are to judge from G. W. MOller's 

 figures, considerably smaller than in the female. 



Under these circumstances it is probably somewhat premature to draw conclusions as 

 to the number of the segments in the Protostracods from the number of these 

 chitinous stripes and to assume that the latter are remains of an original segmentation. Is it 

 not equally likely that we are not concerned with a primitive segmentation, but with secondary 

 chitinous stripes developed as a support for the movements of the back of the body? This 

 assiimption seems to me to be supported by the fact that these stripes are developed differently 

 in males and females. In the males, in which the back of the body presumably has a relatively 

 limited power of movement on account of the great development of the penis, the number of 

 these stripes is considerably less than in the females, in which the back of the body is not 

 obstructed in its movement by an appendage of this size. The difference in the shape of 

 the stripes in males and females is also perhaps an argument in favour of this assumption. 

 Chitinous stripes as a support for the movements of various organs are a fairly common phenomenon 

 in the Ostracods. (Other species of Cytherella dealt with by other writers are unfortunately 

 so incompletely described that it is impossible to take them into consideration in this question.) 



In a number of C y p r i d i n i d s we find on the back of the body a number of transverse 

 folds. A\Tiether these are remains of external segmentation is also uncertain. The number of 

 these folds is different for different forms. Cf. also the bristles and hairs on the back of the 

 body of the P o 1 y c o p i d s (G. W. MUller, 1894, pi. 7, figs. 26 and 50). 



The result of the above discussion seems to be that it is still too early to answer the 

 problem as to the conditions of segmentation in the Protostracods. Whether this 

 problem will ever be able to be solved I must leave undecided. In any case more far-reaching 



