the; mycetophilid.^j of north AMERICA. 213 



future more attention should be paid to the structure of the 

 palpi and antennae, position of ocelli, arrangement of setse on 

 thorax and legs, relative wing and leg measurements, claws in 

 some cases, and especially to the hypopygium of the male, for 

 both generic and specific characters. The descriptive works 

 of Dziedzicki, Lundstrom and Riibsaamen, are particularly 

 excellent in regard to the last. For a proper study of the mem- 

 bers of the MycetoyhilidcE it is absolutely necessary to make a 

 caustic potash preparation of the hypopygium. It is impossible 

 from a pinned specimen to determine the form of the parts, 

 owing to the fact that they are usually more or less retracted. 

 I have found Lundstrom's method of preparation simpler than 

 that of Dziedzicki. In this method it is merely necessary to 

 relax the insect, cut off with a pair of scissors the apical seg- 

 ments of the abdomen; immerse in a 10 per cent solution of 

 caustic potash for twenty-four or more hours, soak in water 

 to remove the potash, and finally preserve in alcohol in a tiny 

 vial bearing the number of the specimen. Besides its sim- 

 plicity this method oft'ers a further advantage in that the 

 abdominal segment which still is attached to the hypopygium 

 offers a hold for the needles in manipulating and arranging the 

 part under the binocular dissecting microscope. Slide mounts 

 alone are not desirable since it is necessary to be able to turn 

 the object in order to see it from all sides. 



The general shape of the hypopygium is that of a cup open- 

 ing posteriorly, the cavity of which is the genital chamber. 

 This cup, which is formed of the sclerites of the ninth segment, 

 is so produced that its margin usually extends beyond the tenth 

 segment which morphologically terminates the abdomen. The 

 tenth segment bears the anus and is usually reduced to a small 

 membranous lobe. Attached to the posterior rim of the 

 hypopygium are several lobe-like appendages which are vari- 

 ously formed or modified. The body of the segment is made 

 up of a dorsal, ventral and two lateral sclerites. From the 

 floor of the genital chamber arises the penis with its variously 

 modified guards. Although several hundred preparations have 

 been made, owing to the complexity of structure I am not 

 yet certain of the homologies of the parts of some of the genera 

 and pending this investigation I must be content in the descrip- 

 tive work which follows to confine myself to noncommittal 



