studies on marine Ostranods 93 



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

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

 the only locomotory organs. 



The families Nesideidae and CytJieruiae are, as G. W. MCller wrote in his monograph, 



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



They are, however, not slow like the C y t h e r e 1 1 i d s, 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 helj) or 



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



Cythereis, Krithe, etc., this antenna 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 y 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. MOller has pointed out, this limb has in 



the Cytherids a powerful spiiming 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-stratimi. These threads are, as G. W. MCller has shown, of great 



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



etc., as it is on them that the posterior limbs obtain a hold during'climbing. 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 fi'om 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 they might seem to be best fitted for a backward crawling movement, 



a structure that is presmnably to be considered as an adaptation to the climbing movements 



described above. S0iiEN JEXSEN* even assmned that they were situated in a direction quite 



the opposite of that which they actually have and he accordmgly 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 kaum moglich, sich daruber GewiBheit zu verschaffen.'" G. ALM, in 



his work quoted above, describes how tlie C y p r i d s use their sixth limb in crawlmg. The 



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



* „Biologiske og systematiskf UiidersOfielsiT ovi'i' FiTskviinds-Ostraioder.- Natli. Mrdd. Kjelii'Mliavn. 



