416 CRUSTACEA ENTOMOSTRACA. 



body, for the attachment of the antennary muscles. They are 

 indicated at a later stage in the plane of the paired eye in 

 Fig. 270. 



After a short time passed in the cypris stage, now swimming 

 rapidly and now crawling by means of its leg-like antennae, the 

 larva becomes fixed with the ventral margins of the shell 

 applied to the object to which it is attached, and passes into 

 the pupal stage. 



The attachment is effected by the secretion of the cement 

 glands by which the discs of the first antennae are glued on to 

 the object selected by the larva for its resting-place. During 

 this stage the compound eyes, the abdomen and other organs 

 undergo a retrogressive metamorphosis, while the adult structures 

 are developing. The curvature of the axis of the larva already 

 marked, undergoes a considerable increase, the region bearing 

 the mouth becoming directed still further backward (Fig. 270). In 

 this marked flexure of the region of the body which lies about the 

 alimentary canal, the anterior part, bearing the antennae and con- 

 taining the cement gland, the compound eyes and the rudiments 

 of the ovaries, does not participate. The result is that a partial 

 separation of the body into two divisions is brought about ; 

 the space between the dorsal body wall and the carapace 

 extends downwards (if we regard the ventral edge of the shell 

 as horizontal, as in Fig. 269) and finally downwards and back- 

 wards, as it follows the curvature of the posterior region, until 

 what we have called the dorsal fold (Fig. 271, A and B, x) comes 

 to lie near the ventral surface of the larva. 



When the pupal skin is shed the remains of the compound 

 eyes, the larval swimming appendages and the above men- 

 tioned apodemes for the insertion of the antennary muscles 

 are shed with it. As the result of the shedding of these 

 chitinous plates a deep notch is left (Fig. 271, B, y) in the 

 ventral side of the anterior end, lined but not filled by the 

 delicate cuticle of the succeeding stage. The subsequent growth 

 of this region is accompanied by a further change in the relative 

 positions of the parts. The notch gradually opens out (Fig. 

 271, C), with the result that the part of the body posterior to 

 it swings round through nearly a right angle, the ventral margin 

 of the shell being now directed perpendicular to the surface 

 of attachment, instead of parallel to it as heretofore. 



