54 INVERTEBRATE ZOOLOGY 



The nauplius larva is of great theoretical significance. It 

 appears as the youngest, free-swimming larval stage of almost 

 all the entomostracans and of several of the nialacostracans, 

 and those malacostracans which are born in a later period of 

 their development pass through a nauplius stage (i.e., a stage 

 in which the body is unsegmented and bears three pairs of 

 appendages) while they are still in the egg. This universal 

 occurrence of the nauplius larva seems to indicate that it 

 repeats substantially the structure of the primitive ancestor of 

 all crustaceans. 



In its further development and growth the nauplius larva 

 increases in size, gradually becomes segmented, and acquires 

 new appendages, its growth and the specialization of its organs 

 advancing from the anterior towards the posterior end. The 

 appendages, which were originally typical, unmodified crusta- 

 cean appendages, become differentiated to form the first and 

 second pairs of antennae and the mandibles, and finally the size 

 and structure of the adult are attained. 



Exercise 2. Look for several nauplii which are somewhat 

 advanced in development and draw outlines of them. 



