396 



COMPARATIVE AXATOMY 



CHAP. 



is especially the case with the 1st maxillipedes, and the rudiments of the last 2 

 ambulatory feet. The Phyllosoma shows in a specially striking manner the character 

 of a pelagic larva. 



Development of the Brachyura. 



A very characteristic Zoaea larva (Fig 



267) is hatched from the egg. Its dorsal 

 shield is marked by the 

 possession of long spine-like 

 processes, among which a 

 frontal, 2 lateral and 1 dorsal 

 are never wanting. All the 

 head limbs are present. Of 

 the thoracic limbs we find 

 only the 2 anterior pairs of 

 maxillipedes ; the other thor- 

 acic limbs, as well as that 

 part of the thorax to which 

 they belong, are wanting or 

 are only found in their first 

 rudiments. The abdomen is 

 segmented, and ends in a 

 fork, but has no appendages. 

 In the later Zoasa stages 

 the 3d pair of maxillipedes 

 appears, the 5 ambulatory 

 feet arise as uniramose limbs 

 (without exopodites), and 

 the pleopoda begin to form. 

 The Zocea swims principally 

 by means of the 2 biramose 



anterior pairs of maxillipedes, and also by means of the abdomen which, in com- 

 parison with that of the adult, is 



elongated and well developed. 



The older Zocca changes into a 



Megalopa larva (Fig. 268). 



This larva, but for the more 



strongly developed abdomen and 



the pleopoda, already resembles the 



sexual form. The maxillipedes and 



ambulatory feet appear as in the 



adult condition, and it must be 



specially remarked that the ambu- 

 latory feet are never biramose, and 



that the Brachjrura thus do not 



pass through any Schizopoda 



Fig. 267.— Zoasa of Maja, after its moult (after Claus). 7i, Heart, 



Through many moults the Mega- 

 lopa is gradually transformed into 

 the sexual form. 



We need say only a few words 

 about the development of the 

 other Malacostraoa. The Lcptos- 



FiG. 208.— Megalopa larva of a Portunus with abdo- 

 men straightened out, dorsal aspect (after Glaus). 



