NEBALIOPSIS TYPICA 221 



Linder goes further and, as I have mentioned above, states (loc. cit. p. 31) that the filtering 

 mechanism of Nebaliopsls is an even more efficient system than that of Nebalia. He points out that it 

 differs in two respects — first that the eighth trunk Hmb is not fihratory, and secondly that the 

 maxilla, together with the first and second trunk limbs, form a separate filter system. It can only be 

 deduced from this that Linder considers that the Nebaliopsis mechanism evolved directly from that of 

 Nebalia, a fact with which all will agree, and further, that it only shows the two differences which he 

 enumerates. There is, however, another fundamental difference which he has overlooked. In Nebalia 

 the trunk limbs curve backwards so that one limb overlaps the limb behind. In Nebaliopsis, according 

 to Linder's hypothesis, the limbs bend forwards so that one limb overlaps the limb in front. This 

 being so it is clear that Linder's Nebaliopsis mechanism could not have evolved from that of Nebalia, 

 for such an evolutionary process would involve an intermediate stage when the limbs curved neither 

 backwards nor forwards and so would be unable to carry out any filtration. If, therefore, the trunk 

 limbs of Nebaliopsis do filter according to Linder's mechanism, then this would be an entirely new 

 development and this is not what Linder has been arguing. 



There would be the same difficulty here as occurs when it is attempted to derive the malacostracan 

 maxillary filter from the anostracan trunk limb filter (Cannon, 1928, p. 820). Both these are based on 

 typical phyllopodia, but in the former the limb is concave anteriorly and in the latter posteriorly. But 

 what is more important, the functional activities of the limbs are dependent absolutely on these 

 arrangements of the limbs. The same applies to Nebaliopsis and Nebalia. The activities of their trunk 

 limbs, whether actually filtratory or only supposedly so, depend on their arrangement and since they 

 are arranged as mirror images, one pointing forwards and the other backwards, it is not possible to 

 derive one mechanism from another, without postulating an intermediate stage during which the limbs 

 could not function. 



BIBLIOGRAPHY 



Cannon, H. G., 1927. On the feeding mechanism 0/ Nebalia bipes. Trans. R. Soc. Edinburgh, lv, pp. 355-70. 



Cannon, H. G., 1928. On the feeding mechanism of the fairy shrimp, Chirocephalus diaphanus Privost. Trans. R. Soc. 



Edinburgh, LV, pp. 805-22. 

 Cannon, H. G., 1931. Nebaliacea. Discovery Reports, Cambridge, hi, pp. 199-222, pi. xxxii. 

 Cannon, H. G., 1943. On the anatomy of Gigantocypris muUeri. Discovery Reports, Cambridge, xix, pp. 185-244, 



pis. xxxix-xlii. 

 Linder, Folke, 1943. t)ber Nebaliopsis typica G. O. Sars, nebst einigen allgemeinen Bemerkungen iiber die Leptostraken. 



Dana-Report, No. 25. 

 Murray and Hjort, 191 2. The Depths of the Ocean. London. 



Ohlin, a., 1904. tjber eine neue hathypelagisch lebende Phyllocaride. Zool. Anz., Leipzig, xxvii, pp. 59-61. 

 RowETT, Helen G. Q., 1943. The gut of Nebaliacea. Discovery Reports, Cambridge, xxiii, pp. 1-18. 



