264 H - p - KJERSCHOVV AGERSBORG. 



for that purpose as in Aplysis Linnaeus, in which the parapodia 

 figure quite prominently. Forms closely related to the nudi- 

 branchs, such as the gymnosomatous Pteropoda, may be particu- 

 larly exemplified in this connection. These parapodic forms are 

 pelagic per se (vide Kjerschow Agersborg, 1922*;). Although 

 several nudibranchs are pelagic, this habit is secondary, notwith- 

 standing. 



Collingwood ('79) records swimming as a means of locomotion 

 in Scyllea pelagica, and Garstang ('90) for Lomanotus Verany. 

 Kjerschow Agersborg ('19, '21, '22, '22^) reports swimming as 

 one mode of locomotion in Mclibe leonina. But none of the forms 

 as here mentioned are good swimmers although Garstang's state- 

 ment seems to indicate that Lomanotus progresses through the 

 water during swimming. I am unaware of any previous record 

 as to the pelagic habit of Dcndronotus. The assumption may be 

 quite justified that Dendronotus, in spite of its highly developed 

 foot, is pelagic in habit, not only because of the evidence connected 

 with the place of discovery of the particular specimen upon which 

 this discussion is based, but rather on the striking, highly developed 

 method of locomotion, viz., swimming. Melibe leonina, although 

 quite frequently pelagic in habit, is not such an able swimmer as 

 Dendronotus giganteus. The last-named species may, therefore, 

 be more pelagic in habit than it is commonly thought to be. 



Simroth, Fleischmann, Jordan, Bohn, Kiinkel, Carlson, Bieder- 

 mann, von Uexkiill, and others have shown that during ordinary 

 locomotion not only do the muscle fibers of the foot take part in 

 the production of the pedal waves, but also certain muscle fibers 

 of the body-wall. This is more readily understood when one real- 

 izes the relation of the muscle fibers of the body-wall to those in 

 the foot, in terrestrial as well as in aquatic or marine snails. The 

 swimming habit, of course, is not equally developed in all, which 

 is partly due to the general shape of the body. During swimming 

 the muscle fibers of the body-wall act preeminently ; during creep- 

 ing, those of the foot. 



SUMMARY. 



i. Dendronotus giganteus O'Donoghue swims by bending the 

 anterior end of the body sideways to an angle of about 45, pro- 



