42 BULLETIN OF THE BUREAU OF FISHERIES. 



The silk glands (fig. 44) are small and egg-shaped in general outline. Their ducts 

 fuse some little distance posterior to their opening, which is situated just dorsal to the 

 anterior border of the hypopharynx. The shape, relative size, and transparency of 

 these salivary glands, together with the very different functions of the head and mouth 

 parts in the Tanypinae, at least suggest that their function is more exclusively that of 

 a digestive gland than it is in the Chironominae. 



The alimentary canal is developed rather differently in the Tanypinae than in the 

 Chironominae. Miall (1895) figures the alimentary tract for Tanypus maculatus but 

 does not label the parts. In comparing these structures with the drawings of the ali- 

 mentary canal of Chironomus sp. ? given by Miall and Hammond the croplike enlarge- 

 ment so easily distinguished in the Tanypinae (fig. 44, cr) is represented only by a narrow 

 esophagus. The cardial chamber (fig. 44, c) is narrow and sharply marked off, and its 

 surface is covered with longer coeca than in the Chironomus, but, on the whole, not so 

 very different from it. The stomach proper (fig. 44, st) is proportionally shorter and of 

 less functional importance. The remainder of the alimentary canal is quite similar in 

 both subfamilies. 



The food is retained in the crop (fig. 44, cr) part of the alimentary canal when first 

 consumed and is constantly being stirred about by a peristaltic motion. When speci- 

 mens are starved for a considerable time, the food is retained in this part of the ali- 

 mentary tract often for the greater part of a week, which would seem to indicate its 

 relative importance. 



The peritrophic membrane, if present, is very thin and inconspicuous. The author 

 has been unable to discover its presence by gross dissection and has consequently con- 

 cluded that in this respect the Tanypinae are decidedly modified as a result of then- 

 carnivorous habits. From the length of time that the diatoms are retained in the ali- 

 mentary canal it would seem probable that they also are as well digested as they are in 

 the stomach of the Chironominae. As stated above, the digestion in this latter group is 

 quite incomplete and any comparative statement must be relative in its nature. 



It will be clear from the above considerations that the fundamental structures of 

 this subfamily are closely correlated with its peculiar manner of life. It seems probable 

 that this subfamily represents a more primitive type of insect than those included in 

 the Chironominae. This conclusion is based not alone on the free-living active behavior 

 of the larvae, but also upon the pupae, which resemble the pupae of Culex in their manner 

 of life, as well as upon the primitive venation of the wings of the adults. 



SUBFAMILY CERATOPOGON I Nj£. 



This is a widely distributed group. Many of the adults are known as blood-sucking 

 insects, some attacking other insects exclusively and some turning their attention to 

 the higher animals including man, while others appear not to take any food in the 

 adult condition. 



In the larval condition their habits are also variable. Guerin (1833) found the 

 larvae of Ceratopogon geniculatus Guerin and C. flavifrons Guerin under the bark of 

 dead trees in a humid environment. Dufour (1845) found larvae of a species which he 

 identified as Ceratopogon geniculatus Guerin in decomposing onions. Perris (1847) 

 found the larvae of Ceratopogon brunnipes Perris in decomposing mushrooms at the 



