1896. NOTES AND COMMENTS. 3 



to the value and importance of habits in the discrimination of species 

 very closely similar in anatomical structure. Having laid it down as 

 a rule that each species of Perdita visits normally but one species of 

 flower, he remarks, " There is no essential difference between those 

 characters called specific and those called varietal ; in fact, the very 

 same kind of difference which marks species in one group, may only 

 mark varieties or mutations in another. Thus we come to see that 

 the essential distinctions between species are physiological [the italics are our 

 own] , the morphological ones being only valid for diagnostic purposes 

 just so far as they happen to coincide with the physiological." We 

 are not quite sure that we fully understand what " physiological " 

 means here ; the context and instances lead us to suppose the word to 

 mean " habits in relation to flowering plants." The chief examples 

 are the two species, P. zebrata, found only on Cleome semdata, and 

 P. bakercs, occurring on Solidago and Helianthus. These two species 

 are stated to be extremely alike, especially in the female sex, nor was 

 it until a specimen had been taken on Solidago that two species were 

 recognised. It appears, however, that the genitalia have not been 

 examined in this work, except as an afterthought ; and, indeed, the 

 tardy examination of the male genitalia of the two species in 

 question at once revealed " apparently good distinctions." It is some- 

 what startling to find organs which of all others are likely to yield 

 good distinctions so entirely neglected. In the separation of species 

 from species nothing can be more efficient than structural alterations 

 which may render sexual intercourse between diverging groups a 

 physical impossibility. In view of this admission Mr. Cockerell's 

 "physiological species " is an unwarranted and unjustifiable expression. 

 Nevertheless, it shows the importance of accurately observing the 

 habits of living animals, inasmuch as differences being known in this 

 respect may lead to a reasonable suspicion of structural distinctions, 

 and to more careful search among a few examples for features which 

 might otherwise be overlooked or only ascertained by dissection and 

 ruin of every specimen. For instance, if doubt were felt as to any 

 specimen being P. zebrata or P. bakers, a note stating it to have been 

 found on Cleome semdata would at once determine in favour of the 

 former without the extraction of the male genitalia, now that it is 

 known that these present good distinctions. 



Evolving Species. 



It is tolerably clear that Mr. Cockerell is right in recognising two 

 species in the case just mentioned, though he does not attach so much 

 importance to genitalia as others would in similar cases, yet, in dis- 

 cussing those and other instances of like kind which he has treated in 

 like manner, he states, " We have, indeed, the process of evolution 

 going on under our eyes, the puzzling forms being those which have 

 only lately segregated themselves and have not yet developed striking 



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