Apeil 30, 1897.] 



SCIENCE. 



675 



the Corrodentia were also developed. The 

 Corrodentia, and especially the winged forms, 

 are peculiar in many respects and stand 

 by themselves ; but I believe that they are 

 derivatives from the branch upon which I 

 have placed them. I do not consider it at 

 all improbable that in the Corrodentia wings 

 were independently developed, and indeed 

 cannot well explain the peculiar venation 

 on any other theory. 



The Neuroptera are evidently derivatives 

 from the Isoptera stock. Here we have the 

 prothorax well developed in all cases, some- 

 times very long indeed, but always united 

 at the base to the meso-thorax and never 

 movable. The wings are similarly de- 

 veloped, both pairs used in flight, the prima- 

 ries covering the secondaries, but neither 

 pair folded in any way. All the forms are 

 terrestrial, as indeed are all belonging to 

 this branch. In all cases the larvte are 

 predatory and have a similar appearance, 

 in the younger stages at any rate. I ex- 

 clude the Sialidce from this order, because of 

 the movable prothorax and the folded sec- 

 ondaries, and include of our American fami- 

 lies only the Mantispidce-, Clirysopidw, Heme- 

 robiidce, Myrmeleonidm and SaphidiidcB. This 

 branch is one of fragments, and all the 

 groups belonging to it, or orders, if we 

 choose to call them so, are of small extent. 

 They may be considered remnants, and the 

 branch as a whole does not seem to be in- 

 creasing at the present time. It will be 

 noted that as at preseat constituted it con- 

 tains no aquatic species. Its point of 

 origin, therefore, is very close to that from 

 which the Orthoptera and CoZeopfera branched. 



The third series, in which the prothorax 

 becomes much reduced in size and firmly 

 articulated to the meso-thorax, has the body 

 parts as a whole much more closely jointed 

 and globular. The tendency is to bring 

 the origin of the legs close together, and to 

 the loss of the sternum as a distinct part or 

 sclerite between the coxae. The meso- 



thorax becomes dominant and best de- 

 veloped, bearing also the chief organs of 

 flight. As a whole, subject to many ex- 

 ceptions, the tendencj"^ is to the develop- 

 ment of the primaries, which are never re- 

 duced to mere wing-covers and never lose 

 function. The tendency seems to be rather 

 to a decrease in the size of the secondaries, 

 as in Uymenoptera, and to their total loss, as 

 in the Diptera. There is, however, a great 

 deal of variation in this respect, and the 

 most that can be justly said is that in this 

 series the secondaries never become the 

 only, or primary, organs of flight. Another 

 point of very great importance is that here 

 the head is neai'ly always more or less free 

 or well separated, tending to the formation 

 of a distinct neck ; while there is never any 

 insertion of the head into the prothorax. 

 This fact will become very striking when 

 the orders that are placed here are com- 

 pared with those in the other section, and 

 this difference in the articulation of the 

 head has never been, in my opinion, suffi- 

 ciently emphasized in our classification of 

 the orders. It is closely correlated with 

 the decrease, in size, of the prothorax. 



In mouth structure the tendency is all in 

 the direction of galear development in the 

 maxilla, while the lacinia becomes con- 

 stantly less important. In the Diptera, in 

 Avhich this series finds its highest develop- 

 ment, the galea predominate over all other 

 mouth structures. In the Hymenoptera the 

 galea is always most highly developed, and 

 particularly so in the bees, the most com- 

 pletely differentiated of all in the order. In 

 the Lepidoptera the galea alone is developed 

 into a functional organ, and in those net- 

 veined orders in which the mouth parts are 

 not rudimentary merelj' the galea is at 

 least as well developed as and never subor- 

 dinated to the lacinia. The orders in which 

 I placed in this series are Odonata, Ephe- 

 merida, Triehoptera, Mecoptera, Hymenoptera, 

 Siphonoptera and Diptera. 



