Stii(lii\s on inarinp Ostracods 93 



on the two pairs of antennae. These have been developed into real small digging shovels. If 

 one leaves the furca out of consideration, these limbs are on the whole to be considered as 

 the only locomotory organs. 



The families Nesideidae and Cytheridae are, as G. W. MOller wrote in his monograph, 

 1894, p. 16 ,,vollstandig an den Grund gefesselt und durchaus unfahig zum Schwimmen". 

 They are, however, not slow like the Cytherellids, but in most cases crawl about fairly 

 rapidly on the bottom or on water plants. Unlike the C y p r i d s they obtain no help or 

 only very slight help from the first antenna in crawling. In a number of forms, e. g. Cytkere, 

 Cythereis, Krithe, etc., this antejina is used chiefly for thrusting obstacles to the side, e. g. grains 

 of sand, etc.; in other forms, e. g. Nesidea, Sclerochilus and Paradoxostoma, etc., it is to be 

 regarded almost exclusively as a sensory organ. But whatever may be the case, this limb 

 does not help to produce a stable and comparatively easy crawling movement in these two 

 families. Looking at it from this point of view it is not surprising that in these families the 

 limbs that have a rather slight significance or none at all in locomotion in the C v p r i d s, 

 namely the three posterior ones, have been more differentiated as locomotive organs. The fifth 

 limb has been lengthened and does not take any part in mastication. The seventh limb is a 

 typical, elongated crawling leg and does not point upwards as in the C y p r i d s. The second 

 antenna in these forms is one of the most important crawling organs; it is this appendage 

 especially that draws the body forward. As G. W. MtJLLER has pointed out, this limb has in 

 the Cytherids a powerful spinning gland, opening out on the point of the exopodite. From 

 this gland a fine thread of a sticky, quickly stiffening, substance is pressed out (as in spiders) 

 and is attached to the sub-stratum. These threads are, as G. W. MtiLLER has shown, of great 

 importance in locomotion, especially in climbing down steep and smooth objects, e. g. algae, 

 etc., as it is on them that the posterior limbs obtain a hold during'chmbing. It is obvious that 

 there must be several pairs of legs to keep the animal safely attached during the alternate 

 seizing and releasing that takes place while climbing along these steep objects and to prevent 

 it from falling outwards and sinking to the bottom, as these animals have not, as has been 

 pointed out above, any first antenna, like that of the C y p r i d s, which by means of its natatory 

 movements is able to keep the body pressed against the sub-stratum. The three posterior 

 limbs can, however, be also used in crawling on horizontal sub-strata. They are, as we know, 

 built in such a way that the}' might seem to be best fitted for a backward crawUng movement, 

 a structure that is presumably to be considered as an adaptation to the chmbing movements 

 described above. S0REN JEXSE\* even assumed that they were situated in a direction quite 

 the opposite of that which they actually have and he accordingly also assumed that they were 

 used as ordinary crawling legs. After a correct idea of their direction was obtained, the idea 

 of their function was also altered. G. W. MULler, for instance, writes in 1894, p. 16: „Sie 

 dienen zum Anklammern. Auch hier scheinen sie gewohnlich nicht zum Fortschieben benutzt 

 zu werden. Doch ist es kamn moglich, sich dariiber GewiBheit zu verschaffen." G. ALM, in 

 his work quoted above, describes how the Cyprids use their sixth limb in crawhng. The 

 same crawling movements are carried out by the three posterior limbs of the C y t h e r i d .s 

 * „Biologisk'' og systematiski' Undersogelsi-r ovir, FiTskvatuls-Ostratoder.- Natli. Mtdd. Kjeboiihavii. 



