256 CRUSTACEA. 



with a well-developed arterial system, and is provided with one pair 

 of venous ostia. 



Later Calyptopis stages (Fig. 117 C) are distinguished from those 

 just described by the more distinct development of the rudiments of 

 the eyes which are still hidden under the dorsal carapace, and by the 

 full segmentation of the body. Not only is the thorax (th) divided 

 into seven (short) segments, but the abdomen also (a-^-a^) appears 

 fully segmented In the last of these stages, the sixth pair of 

 pleopoda (a 6 ) are developed as freely projecting lateral wings of the 

 caudal fin. 



If we compare the series of Calyptopis stages with the other stages 

 of Malacostracan larvae, we must class the younger Calyptopis stage 

 with the Protozoaea, the older with the Zoaea. The Calyptopis 

 stages, however, differ from these in the absence of the second pair 

 of maxillipedes which have not yet developed. 



The later stages, known as the Furcilia stages, are characterised 

 above all by the complete development of the stalked eye which is 

 now movable, and which from this time onwards is not covered by 

 the forward extension of the dorsal shield, but projects freely through 

 an indentation at its edge. A corresponding change is found in the 

 part of the cephalic shield lying between the eyes, which is gradually 

 transformed into a frontal plate running out into a point to form a 

 rostrum. While the six anterior pairs of limbs still retain for the 

 time the shape seen in the Calyptopis stage, the missing posterior 

 limbs are developed, the first Furcilia stage showing the rudiments 

 of the second pair of maxillipedes and of the first pair of abdominal 

 limbs. The other abdominal limbs develop very soon, while the 

 third maxillipede and the ambulatory thoracic limbs, as well as 

 the branchial rudiments belonging to them, appear more gradually 

 in order from before backward. At the same time, in Euphausia, 

 the rudiments of the eye-like luminous organs at the bases of the 

 limbs develop. 



The most characteristic feature of the Cyrtopia stage is the change 

 in the shape of the antennae, which from this time are no longer 

 used as oars, but approach the adult form. The two flagellate branches 

 of the first antenna have lengthened considerably and have become 

 Biented into many rings. In the second antenna, the transformation 

 of the endopodite into the flagellum, and of the exopodite into a 

 scale, are noticeable. Through the completion of the number of 

 limb-rudiments and the development of the last thoracic limbs, the 

 Cyrtopia larva passes gradually into the adult form. 



