SECT, xi DEVELOPMENT 165 



not because it is phylogenetically older, but because 

 its functions are more useful to the free-swimming but 

 not at first independently feeding larva. In the larva 

 of L. productus rudiments of the paired eyes are dis- 

 tinctly visible. The excretory functions of this larva 

 are entirely carried on by the large round or oval patch 

 of glandular hypodermis called the neck- or dorsal- 

 organ (see Fig. 38, and Appendix V.). Lastly, return- 

 ing to the gradual development of the Nauplius into 

 Apus without metamorphosis, we cannot help repeat- 

 ing that in itself it is a strong argument in our favour 

 that the Nauplius is but the young Apus, and Apus 

 but an adult Nauplius (cf. Figs. 34, 39, 41, and 

 Frontispiece). 



One of the chief features, however, in the gradual 

 development of the Nauplius into an Apus is the 

 regular formation of new segments in front of the 

 anal segment as in the Annelid, and the cessation of 

 growth in Apus before the full number of inherited 

 and rudimentary segments are fully developed. Apus 

 is thus, even when adult, little more than a large 

 Nauplius with its posterior segments in front of the 

 anal segment fixed throughout life in their larval con- 

 dition. The significance of this fact is very great, 

 it shows so conclusively that Apus is a primitive 

 form, that we cannot refrain from repeating our 

 explanation of its morphology. The very fact 

 which has been supposed to be an index of the high 

 specialisation of the Apodidae, />., the great number 

 and peculiar arrangement of the limbs, is in reality 

 one of the strongest proofs of the undifferentiated 



