48 PHYLUM ARTHROPODA 



ages) while they are still in the egg. This universal occurrence 

 of the naupHus larva seems to indicate that it repeats substan- 

 tially the structure of the primitive ancestor of all crustaceans. 

 In its further development and growth the nauplius larva in- 

 creases in size, gradually becomes segmented, and acquires new 

 appendages, its growth and the specialization of its organs 

 advancing from the anterior toward 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. 



