214 



THE CANADIAN SPORTSMAN AND NATURALIST. 



the season when they were abundant. The 

 chief interest of the subject, however, centres 

 in the fact that some species are ahvays rare. 

 Sometimes this may be partly accounted for by 

 the scarcity of the food plant, or by their be- 

 ing subject to attacks of parasites to an unusual 

 degree, but still there may be other reasons. 

 Are such species dying out ? And will they 

 in a comparatively short time become extinct 

 from purely natural causes? It is generally 

 admitted that all animals receive at birth a 

 vital impetus, sufficient to ensure their living 

 for a certain period of time, which varies in 

 length according to the species. That is, when 

 not tainted by hereditary disease. This impetus 

 carries each individual through a certain pro- 

 gress of growth, maturity and old age, provided 

 accident or fatal illness does not intervene. 

 In the case of man, this period is about seventy 

 years. Yet we know that many a man, 

 blessed with a vigorous constitution, is as 

 strong and healthy at eighty as others are at 

 sixty, a result due in a great measure to a dif- 

 fered in inherent vitality. This is the case 

 with c 1 1 E.iimals, including insects. The lat- 

 ter live out their allotted time and die of old 

 age, just as men do. Sir John Lubbock de- 

 scribes the death of his pet wasp as being evi- 

 dently from this cause. And here, I may say 

 that the Hymenoptera have among them in- 

 sects which live longer than any other in the 

 perfect state. Sir John Lubbock has had ants 

 seven years old in his formicaries. Now, as 

 there is an individual vitality in animals, giv- 

 ing to each a certain life period^ which varies 

 according to the species., may there not also 

 be a specific vitality ? May not species, as 

 well as individuals, have an allotted time, and 

 grow old and die ? If such is the case,insects 

 would give the best opportunities of studying 

 the subject. The rapidity of the changes they 

 pass through, and the quick succession of 

 generations, would lead us to expect that, in a 

 comparatively short time, many species might 

 run their course, and become extinct from 

 mere loss of specific vitality. The speculation 

 is an interesting one, but its value will not be 

 proved for a long time to come. I lately met, 

 however, with an item in an old number of the 

 " Zoologist," (page 7095) which seems to have 

 some bearing on the subject. It is a commu- 

 nication from Dr. Wallace to the Entomologi- 

 cal Society of London, and reads as follows : 



Remarks on the occurrence of Rarer British 

 Sphiiigidic. 



l< The fact that in many female Sphingidre 



captured in Great Britain and Ireland, in the 

 autumn months, no ova have been found, in- 

 duces the question as to whether some species 

 may or may not be continuously indigenous. 

 Many think that the absence of ova in the 

 female is merely a question of time, as in the 

 case of A. atropos, the females of which, no- 

 toriously devoid of eggs in the forced autumn 

 specimens, are found in June depositing ova, 

 whence the brood is perpetuated. Others 

 maintain that it is a question not of time only, 

 but also of place ; for taking S. convolvuli, 

 females of which are constantly taken in the 

 autumn months, almost invariably without 

 eggs (in 1846 and 1859 the species occurred 

 most freely ; one individual took nearly fifty 

 specimens in 1859, all the females of which 

 were destitute of ova). In this case either a 

 female is hatched in the autumn with eggs, 

 hybernates and deports ova in the spring, or 

 emerges in the spring from the pupa, or else 

 specimens ffy over from abroad and deposit 

 ova in this country. I would ask has 

 S. convolvuli ever been taken or observed in 

 the spring or early summer in this country, 

 and if so in what condition or of what sex? 

 Are we to look for a development of females of 

 D. Hneata without eggs, in the autumn montns, 

 if a hot summer intervenes ? A series of 

 observations carefully made as to time, place, 

 condition, sex, and also as to the complete 

 development of sexual organs of any or all of 

 the rare Sphingida?, would help to resolve the 

 question. I commend it to the attention of 

 entomologists." The interesting fact here 

 stated is, that numbers of females among the 

 rarer Sphingid;v> in England, taken in autumn, 

 are destitute of ova, and consequently incap- 

 able of continuing the species. Dr. Wallace 

 seems to imply that hot weather is a cause of 

 the phenomenon, the absence of ova being a 

 result of the forcing process. May there not 

 be other and more important causes working 

 with this to bring about such a remarkable 

 result ? From what we know of the develop- 

 ment of insects, the effect of an abnormal 

 degree of heat, (within certain limits) on the 

 pupa, is merely to hasten the appearance of 

 the imago, and not to interfere with the perfec- 

 tion of its organs. It seems probable, there- 

 fore, that this failure in the due development 

 of these most important organs is owing to a 

 weakness in the specific vitality of these moths, 

 tending to their complete extinction. A 

 strong instance is that of & convolvuli. Dr. 

 Wallace asks if it has ever been taken in the 



