AMERICAN OHTUOl'TERA. 235 



o^ iLM\oiN <.iicoisf: LocrNifs. 



HY J. L. HANCOCK. 



The theory of (le.<i'eiit implies that iiKMlitication of t'onii is ij.i-:i(hi:il, 

 uikI that iiiteriuediate series have existed between any two i'ornis that 

 might he chosen. But when c.risfin;/ forms are broiiirlit to<>etlier in 

 which connecting links ha\'e perished ni'oups can he pia<'ticailv sepa- 

 rated for convenience. When two forms are in dispute spetMlically 

 the (leHnite way of determining \vhether they are distinct or not i.s 

 to observe if they interbreed. This means, oftentimes, a long delay 

 in confirming the validity of species after new discoveries are made. 

 We can, iji the absence of such proof, resort to the systematic study 

 and comparison of characters. The breaking in on the attending 

 series of evolutionary changes in nature allows, by induction, a dis- 

 tinction to be made of species by the exclusion of inconstant varia- 

 tions of structure. A large series of specimens of a common nj)ecies 

 of grouse locust will illustrate, viz. : 1. A generation of individuals 

 closely resembling each other, but with structural peculiarities mani- 

 fest as slight departures in each specimen from the parent ( individual 

 variation); 2. A group composed of examples in which slight, but 

 similar lines of departure of structure occur (varieties) ; 3. Another 

 in which analysis confirms progressive fixation of structure (insipient 

 or sub-species) ; 4. Lastly, stronger though variable structural pecu- 

 liarities recognizable as common characters (species). Besides, tiieri' 

 are atavic; dimorphic forms which are subordinate to si)ecies. The 

 advent of modern discussions in evolutionary doctrines has made it 

 particularly important to note the differences or plasticity in the or- 

 ganism. The contention that constant structural j)eculiarities be 

 used in separating species leaves out those forms falling under the 

 classes one to four. There has been a notable indifference to the 

 grouping and characterization of species now in tlie actual process 

 of evolving as in those outlined above. In the interest of advancing'- 

 scientific knowledge their consideration is of much interest. Where 

 mention is made of " species" is this group, the Tettigidie, we are a 

 good way along in permanency of characters. The great degree of 

 variation occurring in the grouse locusts is well known. In so shoit 



TKANS. AM. KNT. SOC. X.Xiri. JULY. 1»96 



