June 16, 1899.] 



SCIENCE. 



837 



lateralis of Newstead's cUffinis may be cited, 

 lateralis merely representing the immature 

 stage of Comstoek's cydoni(e. 



In the matter of individual variation 

 this is just as notable in scale insects as in 

 man or other animals. The two halves of 

 the anal plate of a female Diaspine are 

 never exactly alike, and often vary within 

 quite wide limits. In different individuals 

 from the same colony such variations are 

 still greater. Fortunately, however, the 

 characters of real value in this group of in- 

 sects are much more constant than one who 

 had not studied the subject would suppose, 

 even in the case of material representing 

 the same species from widely separated quar- 

 ters of the world, and on totally dissimilar 

 food plants. In the Diaspinse, perhaps 

 more markedly than in most other groups of 

 insect, the specific characters are sharply 

 and satisfactorily defined, and, hence, the 

 less excuse for the cumbering and befogging 

 of the literature which has resulted from 

 careless, hasty and thoughtless work. 



Minute differences in the pores or glands 

 and appendages, or in the lengths of the 

 joints of antennae or legs, are usually indi- 

 vidual and would often make two species 

 of the same specimen if the latter were cut 

 in half in the line of the main axis of the 

 body. To return to an illustration already 

 employed, one might as well describe men 

 as distinct because they have Eoman or 

 Greek noses or short or long chins. 



In other groups than the Diaspinse I 

 cannot speak from careful personal study, 

 but I have the gravest doubts of the value 

 of descriptions based on slight variation in 

 the lengths of the joints of legs and anten- 

 na, all of which must be subject, within 

 specific limits, to variation with the age of 

 the specimens and with its condition as to 

 abundance or scarcity of nourishment. In 

 this connection I cannot do better than 

 quote the views expressed relative to the 

 group Lecaninse, by Mr. Theo. Pergande, 



in a recent letter to a correspondent, views 

 in which I heartily concur. He says : 



" With regard to the difference in length 

 of one or the other of the antennal joints, 

 -+ * * * * I will say that it is simply 

 individual variation ; even in the same 

 specimens the comparative length of 

 either of the joints of both antennae 

 varies frequently, more or less. There is 

 generally, also, a more or less perceptible 

 variation in size, color and shape, in the 

 same species, dependent in a measure on 

 the food plant on which it may have estab- 

 lished itself, and also on the locality. Old 

 specimens, which have attained their full 

 growth and have died a natural death, are 

 generally darker, if prepared for the micro- 

 scope, than younger individuals of the same 

 stage, and with all the pores of the derm 

 much more distinct. As to the shape of 

 the individual scales and their sculpturing 

 I find in our material of typical specimens 

 of Lee. armeniaeum the same variations as 

 those mentioned -i= * * * * To con- 

 sider every slight variation of specific value 

 would lead to endless species which nobody 

 would be able to recognize, and which 

 would cause endless trouble in the stiady of 

 this most difficult group of scale insects." 



The writer trusts that the foregoing criti- 

 cisms will be taken in the kindest spirit, as 

 they are intended, and he does not wish it 

 to be thought, for an instant, that he fails to 

 recognize the learning and enthusiasm 

 shown by the prominent workers in the 

 Coccidfe, by no means all of whom have 

 been equally guilty, and whose work in the 

 main h&a been most excellent, and com- 

 mands the heartiest approval, but, having 

 experienced the great difficulty and labor 

 necessary to discover and correct errors 

 arising from the conditions criticised, the 

 need of calling attention to them seems 

 imperative. (.. L. Marlatt. 



Department of Agriculture, 

 Washington, D. C. 



