496 O. W. HYMAN 



Description of the Megalops (figs. 14 and 15). When the fifth 

 zoea molts to the form of the megalops, a profound change occurs 

 in many of the parts. The contours of the cephalothorax and 

 the abdomen are both changed. Throughout the zoeal stages 

 the cephalothorax is flattened from side to side. In the megalops 

 it is flattened dorso-ventrally . The abdomen is cylindrical in 

 the zoea and now becomes flattened dorso-ventrally also. The 

 changes in many of the appendages are still more striking. The 

 animal suddenly becomes well equipped for an active predatory 

 existence. The sensory structures of the antennule and the 

 antenna are practically in the adult condition. The chelae are 

 efficient structures for securing the prey and the maxillipeds are 

 transformed into masticatory organs. The pleopods are now de- 

 veloped into powerful swimming organs and the animal darts 

 swiftly about. 



The antennule (fig. 26) is now composed of a large basal portion 

 and a terminal process of four segments. The basal segment 

 bears the statocyst which can be distinguished through its walls. 

 The ultimate and penultimate segments bear from five to seven 

 olfactory hairS each. The antennule has now reached what is 

 practically the adult condition. The antenna has undergone a 

 striking change (fig. 34). The zoeal lateral spine and lateral 

 segment are absent. The flagellum is composed of eight small 

 cylindrical segments and is borne at the tip of a basal portion of 

 three larger segments. The antepenultimate segment of the 

 flagellum bears four or five long tactile hairs and the terminal seg- 

 ment two or three. 



The mandible (figs. 40 and 41) has reached practically the 

 adult condition, as it now bears a three-jointed palp. The first 

 maxilla (fig. 51) shows few changes. Its basal median lobe bears 

 more spines and is enlarged. The joints of the palp are obscm-e 

 and its segments somewhat shriveled. The hairs on the lateral 

 border of the basal portion have the same form as the hairs on 

 the epipodites of some of the appendages posterior to it. The 

 second maxilla (fig. 60) has undergone changes similar to those of 

 the first. The palp has lost its hairs and joint and appears as a 

 smooth lobe of the basal portion. The scaphognathite is larger 

 and has more hairs along its border. 



