00 



M. T. THOMPSON. 





FIG. 



Fourth larva 



" C" were ; head 2.5 mm., thorax 132 mm., abdomen 



The "head" was 1.8 mm. broad at the widest; the horns spread 



2 mm. 



In the fourth member of my series " D " (Fig. 3) the chief 



change is the further progress of the shifting upward of the 



anterior face of the "head." The tips of 

 the rostrum and anteriormost tubercules 

 are visible from above as before. The 

 antennae have migrated to the upper sur- 

 face of the "head" and the apices of the 

 second pair are distant from the anterior 

 border. These antennae are adult in form. 

 A few of the abdominal appendages con- 

 sisted of a main ramus and two minute 

 accessory rami, but the majority of this 

 { f appendages had only a single 



"D" of P. filosa; ven- J 



tral aspect of "the head. accessory branch and the first five c* six 



pairs were uniramous. The " head ' of 



this specimen measured 3.5 mm., the body 130 mm., the ab- 

 domen, 16.5 mm. 



Of the two remaining specimens of the series ; " E," the Woods 

 Hole example, closely resembled " F " (Fig. 4), the last of the 

 primary group. The " head" is now broad anteriorly, but does 

 not as yet approach the rounded form characteristic of the 

 " head " of the adult P. filosa. In " E " the antennae were nearer 

 the anterior margin of the "head" than was the case with " D," 

 but were not visible from below. A trace of the cephalotho- 

 racic border is still present in this anterior dorsal region. The 

 rostrum has disappeared and the venter of the anterior part of 

 the "head" is covered with small tubercles, amid which the 

 tubercules already introduced are lost. In specimen "E" the 

 median one of the older series could just be identified. This 

 specimen also exhibited faint traces of the median eye and the 

 condition of its abdominal appendages was similar to that existing 

 in " D," the six anterior pairs being unbranched, the remaining 

 pairs having a longer outer and a shorter inner ramus. The 

 rami are longer than the rami of " D's " appendages, however. 

 All the abdominal appendages of " F " on the other hand had two 



