IMMATURE SPECIMENS OF PENELLA FILOSA. 



299 



tut* 



specimen was 94 mm. long; of which the head measured 2.5 

 mm., the thorax 80 mm., and the abdomen 11.5 mm. 



The next older specimen (Z?) shows a marked advance in 

 development over "A" (Fig. 2). The cephalothorax and thorax 

 are no longer distinctly demarked from one another and the sides 

 of the anterior portion of the former region 

 are inflated so that a "head" is differen- 

 tiated. On the dorsal surface, in the neigh- 

 borhood of the antennae, a trace of the 

 borders of the cephalo-thorax still persist. 

 In the region of the anterior pair of thoracic 

 limbs, behind the newly-formed "head" a 

 pair of blunt horns have made their ap- 

 pearance. The median eye was not noted 

 in this individual. The antennae and maxil- 

 lipeds are much the same as in stage " A," 

 except that the second antennae are now 

 more chelate. The rostrum is distinctly 

 shifted toward the anterior border of the 

 head and the median tubercule is now rein- 

 forced by a conical tubercule on either 

 side of the rostrum. Whether this pair of 

 tubercules replace the maxillae or not is 

 uncertain. These appendages were not ob- 

 served in the specimen under consideration, 



but the minute palps to which they are reduced were doubtfully 

 traced in the next older specimen mesad from the lateral tuber- 

 cules. The abdominal appendages are uniramous as before. 

 The length of"/?" was 130.5 mm. The "head" measured 2.5 

 mm. long by 1.2 mm. wide, the thorax was 120 mm. long, the 

 abdomen 8 mm. long. 



The third specimen (C] differed from " B " in the still more 

 inflated " head " and in the replacement of the maxillipeds by a 

 pair of tubercules, so that the ventro-anterior face of the " head " 

 now presented five tubercules, one median and four paired. The 

 rostrum of this stage pointed in a line with the axis of the 

 " head " and its tip together with the tips of the anterior pair of 

 lateral tubercules were visible from above. The dimensions of 



FIG. 2. Second oldest 

 larva "B" of P. filosa ; 

 dorsal and ventral aspects 

 of the head. 



