204 THE SCOLYTID BEETLES. 



Exit hurrow. — The exit buiTow is that through which one or many 

 individuals of a developed brood emerge. In the case of ambrosia 

 beetles the entrance may also be utilized as an exit, but in the bark- 

 beetles the exit is usually direct or indirect from the pupal chamber. 



Larval mine. — The larval mine is the food buiTow excavated by 

 the larvae from the point where it hatches from the egg. The indi- 

 vidual mine may be widely separated from or closely approximate 

 to those of other individuals of the same brood, and they may be 

 arranged in groups or those of the entire brood may be connected to 

 form one common larval chamber. 



Larval cell. — The larval cell is excavated by the larvae in the side 

 of the gallery simply to accomodate the increasing size of the body, 

 as in the case of many species of Corthylinse where tho food consists 

 of ambrosial fungi provided by the parent. 



Pupal cell.^-The pupal cell is formed by the prepupal larva or by 

 the pupa itself and is usually located at the end of the larval mine or 

 food burrow of the larva. This is especially true in the case of the 

 barkbeetles or the wood-mining larvae, which latter, as in Micracis, 

 Thysanoes, Scolytus muticus, etc., extend their burrows for a long 

 distance from the bark mines into the wood. On the other hand, 

 certain species of Dendroctonus form the pupal cell in the outer 

 corky bark (JD . frontalis) or in the social larval chamber (Z>. valens), 

 instead of at the end of the larval mine as in D. ponderosse. 



AU of the named parts of the gallery have characters more or less 

 pecuHar to the species or group of allied species. Therefore the gal- 

 leries as a whole, or in their various elements individually, or m various 

 combinations, are worthy of special attention in the search for taxo- 

 nomic characteristics. 



CLASSIFICATION OF THE GALLERIES. 

 Egg Galleries. 



In an attempt to classify the scolytoid egg galleries it is impor- 

 tant to remember that the newly excavated galleries in which the 

 first sets of eggs are deposited are more reliable in suggesting the type 

 or group they represent than are the older ones, because in some 

 species they may be so radically changed and confused by secondary 

 branches and the intermingling of two or more galleries that the 

 characteristic type may be obscured. 



Larval Mines. 



The larval mines furnish, to a limited extent, evidence of pro- 

 gressive modification, as is found in Dendroctonus. The larval mines 

 in most of the Cryphalinae are without distinctive characters, while 

 in Ipinae, Hylesininae, and Scolytinae their symmetrical arrangement 



