360 Introduction to Animal Morphology. 



the remains of the ancestral dorsal spine of the Zoea*. These 

 transformations take place in the egg, and the young has 

 assumed its adult form on its emergence. 



Fig. 42. 



Xiphargus Kochianus ; Niphargus fontanus. 



The families are : i. Gammaridae head small ; antennae 

 many-jointed ; maxillae 4-5 jointed ; some (Ceraphis) build 

 nests of seaweed, &c., like Caddis cases, and most swim on 

 their sides. Orchestia and Talitrus, Sandhoppers, have short 

 antennules, and the third thoracic limbs chelate. Gammarus, 



* The Ancestral Zoea was of the type of the Archizoea, whose descend- 

 ant is the pupa stage of the Cirripede rather than the specialized Zoea, 

 of the crab. The preceding Nauplius resemble that of the Copepod (the 

 Arcliinauplius). 



