VI BRACHYURA—-LARVAL HISTORY 183 
the Glaucothoe of the Pagurids, resembles a small Galathea 
or Porcellana, the abdomen being still large and untlexed 
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 
shght progressive change in 
structure, especially in the 
male, at each successive moult 
of the individual. The Mega- 
lopa of Corystes cassivelaunus 
is pecuhar 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 
less reduced in both sexes Fic. 125.—Later stage (Megalopa) in the de- 
‘ velopment of Corystes cassivelaunus, x 10. 
than in other Brachyura 5 A, Antenna; Ad, 3rd abdominal segment ; 
there is a common orbito- C, great chela; 7'.5, last thoracic appendage. 
(After Gurney.) 
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eyes and antennae are withdrawn, instead of a separate one on 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; Claus held that they proceeded from a Galatheid 
1 Bouvier, Bull. Soc. Philomath. Paris, (8) viil,, 1896. 
