Studips on marine Ostrarods 



37 



Fifth limb: — According to the first of the methods of explanation just 

 mentioned this limb would in my opinion be explained morphologically as follows: 



Family Polycopidae: The fifth limb in this family is of a comparatively simple structure 

 and it is possible that a thorough study of it — as in the case of the second antenna, the mandible 

 and the maxilla — may contribute considerably to a correct explanation of the somewhat more 

 complicated structure of this limb in other Ostracod groups. On the other hand, however, it 

 is by no means impossible that this limb in the P o 1 y c o p i d s is to be considered as a type 

 that has been simplified in a number of respects; this is supported perhaps bv the fact that 

 the two following limbs in this group have been quite reduced; cf., in addition, chapter II of 

 this treatise for the type of the fifth limb in the primitive s t r a c o d s; in other respects it 

 is perhaps of a type that is secondarily somewhat complicated. 



According to G. W. MiJLLER the fifth limb of tlie P o 1 y c o p i d s consists of ,.einem 

 undeutlich gegliederten Stamm, der am Ende 2 kurze ungegliederte Fortsatze (Exopodit 

 und Endopodit?) tragt" (1894, p. 62). This opinion coincides with what I have called in this 

 treatise the first method of explanation. According to this we thus see that this appendage 

 too is to be considered as a biramous limb, although of a less marked type; it resembles rather 

 closely the foliaceous type on account of the protopodite's strongly dominating over the 

 verruciform, unjointed* branches, the exopodite and the endopodite, which are certainly well 

 marked off, but very much reduced. The part which, according to this explanation, corre- 

 sponds to the protopodite always seems to be divided into at least two joints; the proximal 

 one of these joints is sometimes more or less distinctly two-jointed, i. e. three joints 

 can be distinguished, which are consequently to be denoted as the procoxale, coxale and 

 basale. This limb is furnished proximally with a rather long and narrow vibratory plate, 

 which is furnished with fairly numerous and long marginal bristles; this plate is united 

 throughout its whole length with the outside of the two joints that were termed above the 

 procoxale and the coxale; cf. fig. IV: 1 of Polycnpe frequens (I. W. MUller. — In Poli/copsis 

 serrata G. W. MOller the vibratory plate issues, according to G. W. MOller, 1894, pi. 7. 

 fig. 37, from a narrow base situated proximo-laterally on the joint denoted above as the 

 procoxale, but it seems to me not at all impossible that this organ is, in this form too, 

 attached throughout its whole length to the two proximal joints of the protopodite and 

 that in the specimen investigated by G. W. Mt'LLER (presumably only one specimen was 

 investigated by this writer; cf. his work of 1894, p. 2,39) it was partly detached, during 

 preparation, from the protopodite along the chitinous list that forms its inner boundary. 

 — If the two distal verruciform processes on this limb are to be considered as the exopodite 

 and the endopodite, then it is evident that this vibratory plate must be explained as an 

 epipodial appendage, as G. W. MOLLER has also done. Of the two distal processes the outer 

 one is to be denoted as the exopodite, the inner one — armed with f)nly one bristle in th(^ 

 accompanying figure — as the endopodite. This limb has no endites. 



Family Sarsiellidae: The fifth limb in this family shows a rather close resemblance to 

 that which is found in the family Polycopidae. (It seems to be rather difficult to decide for 



* Sometimes a more or less slight indiration of a division iido two joints rati lie oliserved on the aiitero-inner hraiich. 



Fijih limb. 

 The first method 

 (ij explanatian. 



I'nlycupidae. 



Sarsiellidae. 



