128 [November, 



FURTHER NOTES ON PARTHENOGENESIS IN COLEOPTERA. 



BY J. A. OSBORNE, M.D. 



I send you by this clay's post a parthenogenetically-bred Oasiro- 

 pliysa raphani. It is the second I have succeeded in rearing. Of the 

 first there is some account in this Magazine, vol. xvii, pp. 127 — 130 ; 

 it died after a life of 35 days, and developed "gastrophysm," and 

 on examination it proved to be a female. The present example has the 

 peculiarity of one of the elytra being " cut away " so that they gape, 

 and it has a further defect in the anterior tarsi, which caused embar- 

 rassment and awkwardness when it was alive. This is likewise a 

 female, and although it lived but 17 days, it developed a large amount 

 of " gastrophysm," and paired with two different males ; no eggs, 

 however, were laid by it. The egg that produced it was one of a batch 

 of 42 ; of which lb showed signs of vitality, but only two produced 

 larvae. It was laid by a virgin female on the 14th June, and hatched 

 on the 24th. The first and second moults occurred on July 1st and 

 5th — 6th respectively. The metamorphosis to pupa took place on 

 July 14th — 15th, and the imago appeared on July 23rd. The batch 

 of eggs was the fourth laid by the same mother ; all the batches, of 

 which twelve were laid before impregnation, showed an extraordi- 

 nary amount of parthenogenetic fertility. Of 146 parthenogenetic 

 eggs, six hatched, and the larvae lived a shorter or longer time. After 

 this the insect was allowed to pair with a male, and the subsequent 

 eggs became perfectly viable. 



Nothing has struck me more in these experiments than the per- 

 fectly graduated scale of degree of fertility and developmental capacity 

 in both impregnated and unimpregnated females, and the eggs laid by 

 them. The two series overlap to a considerable extent, and are so 

 continuous as to represent virtually one series, in which the male in-l 

 fluence may be regarded as only a collateral (though, of course,! 

 extremely important) circumstance. The indications of being "addled," 

 which occur in two or three clays, are just as characteristic of eggs 

 laid by impregnated beetles that have escaped fertilization, as in par- 

 thenogenetic eggs. But the great majority of even virgin eggs pass 

 beyond this condition, and at the usual time for hatching are uniformly 

 yellow and of gelatinous consistence, and in these, more minute ex- ' 

 animation often reveals all degrees of imperfect development. Few,] 

 however, hatch, and the larva? usually die very soon. Development j 

 in these is not only imperfect, but is also retarded. 



I consider that the parthenogenesis in Gastrophysa raphani is not 

 at all a rare and accidental circumstance, but may be looked for with 



