Sept., 1902. J 



The Larva of Molanna Cinerea. 153 



The blood system is likewise simple. The main blood vessel is 

 easily distinguishable along the dorsal side. In cross section it ap- 

 pears triangular. Throughout the body there is a great deal of free 



blood. 



The reproductive system is fairly well developed in the larva. 

 The ovaries and spermaries lie in the fourth abdominal segment. 



Mention should also be made of the numerous large oinocytes 

 which lie near the body wall throughout a great part of the abdomen, 

 and of the wing buds which appear very clearly in the mesothorax and 

 metathorax as infoldings in the epithelium. 



Reference has been made to the three tubercles on the first ab- 

 dominal segment. It has long been known that these are retractile 

 and protrusible and so serve to fix the position of the larva in its case 

 and perhaps to regulate the flow of water through the case. ' How 

 this movement is brought about has not been explained. The accom- 

 panying figure shows the simple muscular arrangement by which the 

 retraction is accomplished. Besides these few muscles nothing was 

 found in the tubercles, excepting blood and a small amount of fat. It 

 is altogether probable that the protrusion is effected by a contraction 

 vof the body forcing the blood into the tubercles. 



A New Type of Dermal Gland. 



We conclude our account of the larva with the mention of certain 

 -dermal glands (Fig. 2) which appear in the fourth, fifth, sixth, and sev- 

 enth segments. Unless these glands are not common among the Trich- 

 optera it is surprising that theyshould have remained unnoticed hitherto, 

 for their size as well as the fine staining of which they are susceptible 

 make them very prominent in sections made in any plane of the body. 

 The dermal glands described by Andreas Martynow * resemble these 

 more than any others that are described. That they are essentially 

 different, however, is shown by the following points of contrast : they 

 occur in the posterior segments of the thorax and in all the abdominal 

 segments, they are unicellular and they open through the chitin by 

 means of a canal. The glands of Molanna cinerea, on the contrary, 

 are composed of many cells and have no openings through the chitin. 

 These glands are at the middle of the sides of the body in the lower 

 angle formed by one of the dorso-ventral muscles and thejxxiyjvvall, 



* Martynow, Andreas, Uber einige eigenthiimliche Drusen bei den Tri- 

 chopteren, Zool. Anz., XXIV, pp. 449-455> 5 figs- 



