THE LARVA OF SARCOPHAGA. 165 



into a wide, dorsal lobe and a narrow, projecting, ventral lobe. 

 Between these two lobes is a deep recess into which the anus and 

 po-n -rior -ligmata open. The posterior stigmata are guarded 

 by a large -tigma-plate which has two lobes. Each lobe bears 

 three spatulate chitinous bars (Fig. 4, c.p.} which articulate with 

 six similar bars on the ventral lobe of the segment (Fig. 4, c'. /?'.). 

 The -hape and relation of these dorsal and ventral rhitim>u> bars 

 i<> ea<h "i her are such that I am led to believe that thev function 

 .1- pn -In -unle structures; the lower lobe of tin- se-ment pressing 

 ii- bar- .t'_,iinst the bars of the stigmatic plate can lay hold of 

 the \\all of the excavated region in the skin of the ho-t and thus 

 anrhor tin- larva. The most striking feature to which attention 

 not 1'i-t-n called is the presence of two anterior stigmata 



Fig. 1 These stigmata are fan-shaped struct tin-- \\hicli 



bear -i \euirrii or eighteen papilhe along their let initial edge 



I i. I.). In a specimen cleared with xylol each ot" tl 



niata can be seen to lead directly into a large lateral tr.u lua. 

 "1 1m- the\ are provided with an air-breathing apparatus though 

 they li\e in a thick fluid of suppurated matter which make- 

 liable the i losing of one or more of these iracheal opening or 

 ma\ nei e--it.ite the temporary closing of one of them. In this 

 connection it is interesting to find a transverse tra< heal commissure 

 posterior to the anterior stigmata and another transverse tracheal 

 ( ommi mv anterior to the posterior stigmata. These commis- 

 sures enable both tracheal trunks to get air though for any reason 

 some of the -ligmata may be closed. Thu- the chief tracheal 

 -\ stem consists of a pair of anterior and a pair of posterior stig- 

 mata and two lateral tracheal trunks which are connected by 

 mean- of an anterior and a posterior tracheal commi ure. 



Nothing unusual has been noted concerning the histologv of 

 the tracheal trunks and posterior stigmata. The histology of 

 the anterior stigmata has, however, attracted my attention. 

 These fan-shaped structures are for the mo-t part proliferated 

 masses "f cuticle. The anterior half of the stigma projects 

 be\ond the contour of the body as a stigmatic process. The 

 posterior half lies beneath the surface of the body and is covered 

 by an epithelium which represents the hypodermis modified as 

 tracheal epithelium ( Fig. 8, te.}. l-'mm the posterior margin of 



