174 THE CANADIAN ENTOMOLOGIST. 



developed at the opening of the spiracles in many insects ; they evidently 

 serve the same function. The body of the insect is so thin that towards 

 the edge its dorsal as well as its ventral wall is involved in the production 

 of the fold. The inner ends of the breathing folds enlarge into conspicu- 

 ous chambers, since each fold serves for more than one spiracle. 



There are four pairs of spiracles present in the young of an Aleurodid, 

 though Burmeister recognized only the anterior two pairs. He saw, indeed, 

 the anal pair, but incorrectly identified them as sexual orifices, which he 

 describes as being on either side of the anal opening. At this stage there 

 are no vaginal openings, though the eggs can be clearly seen quite fully 

 formed just anterior to the anal pair of spiracles long before the final 

 moult. The anal opening is on the dorsal surface, and therefore really 

 very far distant from the ventrally placed spiracles. 



The anterior folds are opposite the anterior pair of spiracles, which 

 lie between the bases of the developing front and middle legs ; these pro- 

 ject in regular curves in nearly opposite directions. The tips of the 

 rudiments of the middle legs reach nearly to the base of those of the hind 

 legs ; in these intervals lie the second pair of spiracles. The third pair of 

 spiracles lie just beyond the tips of the rudiments of the hind legs. All 

 these are served with air *by the anterior breathing folds, the three spiracles 

 on each side opening into the three-chambered basal enlargement of the 

 fold on that side. The fourth pair open on a Y-shaped expansion of 

 the aual breathing fold. 



The main portion of the tracheal system consists of a ventral trunk 

 on either side reaching from the anterior to the posterior spiracle, two 

 dorsal girdles connecting with each other the spiracles of the anterior two 

 pairs, and on either side of the abdomen and metathorax a dorsal trunk 

 reaching forward from the anal spiracle to about half way between the 

 second and third pairs of spiracles, where they unite with the ventral trunks. 

 Burmeister recognized the anterior portion of the ventral trunk and the 

 dorsal girdles, and figures them quite accurately, but he did not make out 

 the whole system. 



The finer branches are given off as follows : The anterior spiracles 

 lead into a trunk that almost immediately divides into two main branches, 

 one of which quickly subdivides into about thirty-four long twigs, which 

 spread out fanlike and serve the sides of the body from almost the middle 

 line of the front around the sides to about the middle of the thorax. The 



