BRANCHIOPODA. 197 



setae at the tip. The second antennae (3) are large biramose 

 swimming limbs, each carrying a movable masticatory hook on the 

 basal joint. The endopodite of each of the second antennae is small 

 and has setae at its end, while the five-jointed exopodite has five 

 swimming setae on its inner side. The mandibles (3) are smaller 

 than the second antennae, but agree with them in general structure. 

 The masticatory hook is wanting in the mandibles ; the future 

 masticatory blade (often the sole representative of the mandil^le in 

 the adult) is visible at this stage merely as a slight swelling on the 

 inner side of the protopodite. The endopodite and exopodite are 

 unjointed and carry setae at their tips. The anterior or cephalic 

 region of the body, Avhich carries the Nauplius limbs, is bounded 

 posteriorly by a small dorsal prominence, in which we recognise the 

 first rudiment of the dorsal shield. At the middle of this anterior 

 dorsal region there is a more or less round, sharply circumscribed 

 point, the rudiment of the nuchal gland so widely distributed among 

 the Phyllopoda (p. 151). In the posterior, thoraco-abdominal region, 

 five consecutive thoracic segments have begun to form as transverse 

 swellings {I-V). 



After the first moult (Fig. 93 B), the form of the body is essen- 

 tially changed by the broadening of the anterior region and the 

 elongation of the narrow, cone-like, posterior section. The dorsal 

 shield now covers the tergum of the first thoracic segment. The 

 Nauplius limbs retain essentially the same character. The endo- 

 podite of the second antenna is now two-jointed. On the basal joint 

 of the mandible (3), a strong masticatory blade has developed with 

 teeth on its inner edge, this being covered by the now relatively 

 small upper lip. Behind the mandibles, the first pair of maxillae 

 have begun to appear as simple plates (4). In the anterior thoracic 

 region, two to four lobed rudiments of limbs can be made out. 

 The number of thoracic segments is increased to eight by the 

 addition of new rudiments. At the posterior end of the body, the 

 large furcal processes have developed. Other points of interest in 

 this stage are : the development of the frontal sensory organs as 

 styloid filaments (fs) near the Nauplius eye, the rudiments of the 

 hepatic outgrowths at the wide anterior part of the mid-gut, the 

 greater distinctness of the antennal gland in the basal section of 

 the second antenna, and the rudiment of the shell-gland in the 

 ventro-lateral part of the dorsal shield. 



The third larval stage (after the second moult), reveals lobed 

 rudiments of limbs on the six anterior thoracic segments ; on the 



