BRACHYURA — LARVAL HISTORY 



183 



the Glaucothoe of the Pagi^rids, resembles a small Galatliea 

 or Porcellana, the abdomen being still large and unflexed 

 and furnished with normal 

 pleopods. From this stage 

 the adult structure is soon 

 achieved, though, owing to 

 the continued growth of the 

 Crustacea even after maturity 

 is reached, there is often a 

 slight progressive change in 

 structure, especially in the 

 male, at each successive moult 

 of the individual. The Mega- 

 lopa of Gorystes cassivelmmns 

 is peculiar in the immense 

 production of the second an- 

 tennae, which act as a re- 

 spiratory tube (Fig. 125). 



The Brachyura must be 

 considered under the follow- 

 ing subdivisions : — 



Tribe 1. Dromiacea. 



All authorities are agreed 

 that these ^ are the most 

 primitive of the Brachyura. 

 In them the abdomen is much 



- -Ts 



•Sii^ir 



less reduced in both sexes F'°- 125.— Later stage (Megalopa) in the de- 

 velopment of Corystes casdvelannus, x 10. 

 A, Antenna ; Ab, 3rd abdominal segment ; 

 C, great chela ; 1'.8, last thoracic appendage. 

 (After Gurney.) 



than in other Brachyura ; 

 there is a common orbito- 

 antennary fossa, into which 

 eyes and antennae are withdrawn, instead of a separate one on 

 each side for each organ ; the carapace is often much elongated as 

 in the Macrura and Anomura, and a number of other anatomical 

 characters might be mentioned which characterise the Dromiacea 

 as intermediate between the true Brachyura and the lower forms. 

 There are, however, two views as to the relationship of the 

 Dromiacea ; Glaus held that they proceeded from a Galatheid 



' Bouvier, Bull. Soc. Philomath. Paris, (8) viii,, 1896. 



