DEVELOPMENT 



423 



on the head, called the velum, or sail. The Crustacea, 

 which exhibit so great a range of form in the adult 

 state, all pass through a stage in which they are sub- 

 stantially alike. Forms as different in appearance as 

 barnacles, entomostracans, and prawns hatch out as 

 Nauplii, little oval animals, with a straight intestine, 

 three pairs of legs, and a simple eye (Fig. 373). See 



FlG. 373. Nauplius of Entomostracan (Canthocamptus). See Fig. 57. A, first 

 antenna; An, second antenna; a, anus; L, labrum; O, ocellus; S, stomach. (From 

 Brooks, after Hoek.) Magnified. 



Figures 56, 57, 58, 59. Figure 59 represents the lobster, 

 which does not hatch as a Nauplius, but is not very 

 unlike the prawn. These larval forms are of great 

 interest, because they disclose the relationships of the 

 adult forms, as the gastrula stage hints at the common 

 relationships of all animals above Protozoa. 



