SECT. XI DEVELOPMENT 163 



presence in the Nauplius larva of so many Crustaceans, 

 whether it is afterwards retained by the adult or not, 

 is thus easily explained. Its relatively great size in 

 the larva admits of the same explanation as we gave 

 of the great size of the dorsal shield ; the Nauplius 

 consisting mainly of the Crustacean head of five bent 

 segments, the prostomium is naturally a more pro- 

 minent organ in it than it is later in the adult. 



5. The Bent Intestirie. — As a characteristic of the 

 Nauplius not often mentioned we have alluded to the 

 bent intestine or, in other words, the relative position 

 of the mid-gut and the mouth under the upper lip 

 (see Fig. 37, which is a side view of the Nauplius of 

 Apus showing the position of the parts). We lay 

 stress on this as a characteristic of all Crustaceans, 

 the origin of which is explained by the bent Annelid 

 theory. 



The development of the liver as diverticula of the 

 mid-gut is very clear in Figs. 34, 38, 39, 40. 



The important fact that the nerves for the second 

 antennas spring in the Nauplius from the infra- 

 cesophageal ganglion has already been mentioned in 

 discussing the nervous system. This fact serves as a 

 very striking link between Apus and the Nauplius, 

 Apus showing in this respect a very primitive condition, 

 for though the nerves of the second antennae branch 

 off from the oesophageal commissures, there can be 

 no doubt that the ganglia are infra-cesophageal {cf. 

 Section V.). 



We may perhaps here briefly summarise what has 

 been said about the morphology of the Nauplius 



M 2 



