M. T. THOMPSON. 



the posterior or "genital" thoracic segment being ten times as 

 long as the three anterior rings together. The length of the 

 thorax here shown proportionate to the cephalothorax and abdo- 

 men is in marked contrast to the excessively elongate thorax of 

 the P. filosa larva "A," where the relative lengths of the three 

 body regions are as i' 32' 5'. However, the unlikeness should 

 not be wholly referred to the difference in the ages of the two 

 specimens, because in fully-mature specimens of P. rarians the 



FIG. 5. Youngest, and second and 

 fourth oldest larva of P. various. 

 (From Steenstrup and Liitken.) 



FlG. 6. Bacillus elongatns. 

 (From Lubbock.) 



thorax is proportionally much shorter than with P. filosa. The 

 older larvae of P. varians figured by the Danish observers show 

 a gradual approach toward the proportions characteristic of the 

 adult i' 7' 2' as figured --although the abdomen remains in 

 all disproportionately long. On the other hand, in the P. filosa 

 series the thorax is about twice as long proportionally to the 

 "head" and abdomen as in the adult ; these regions only attain- 

 ing their final dimensional relations later in the course of the 

 development. 



