484 



MATURE 



\Oct. lo, 1872 



insects and crustaceans the unfertilised ova always, or in an enor- 

 mously large proportion, proiluce females only ; v/hilst in the 

 Aphides we know tliat they ultimately produce both males and 

 females. Mr. Darwin has suggested the most satisfactory theory 

 of fertilisation, in assigning to it the object of fusing two life- 

 experiences in the progeny, which thus gains tendencies and 

 acquires impulses from a wider area than does an unfertilised 

 ovum, and is in so far strengthened. Conjugation of two cells, 

 similarly formed but belonging to different individuals (as seen 

 in Conferva; and Gregarina.-) is the simplest arrangement for ob- 

 taining thii end ; the only difference between this and sexual 

 reproduction is that in the latter process one cell seeks, the other 

 is sought ; and this differentiation into active and passive, the 

 wooer and the wooed, commencing in the simplest vegetable and 

 animal cells, persists to the highest r.ink of development. Self- 

 impregnation (if it have a real physiological existence) and par- 

 thenogenesis, have, then, to yield, as chief modes of reproduction, 

 to digenesis, or the concurrence of two individuals ; and this for 

 one and the same reason. Perhaps the apparently anomalous 

 facts that an animal — or plant, as the case may be — develops 

 elaborate motile zoosperms and copulatory organs, merely to 

 fertilise its own egg ; and that other animals and plants develop 

 peculiarly constructed large cells, of a kind apparently especially 

 elaborated in the progress of the general evolution of life, to pro- 

 vide forfertihsation, yet which never are fertihsed — are only to be 

 explained as cases of persistent structures with modified function. 

 In the former case, Monogenesis, being sufficient to or necessitated 

 by the conditions of life, yet avails itself of the apparatus inherited 

 from digenetic ancestors ; whilst similarly, in the second ca.se 

 (pseudova), Monogenesis, having advantages for the particular 

 case (and not being a common phenomenon in the group), instead 

 of making its appearance through new organs, avails itself of the 

 ovary inherited from digenetic progenitors. Thus the unsignificant 

 form of an ovum (unsignificant, that is, so far as monogeny is con- 

 cerned) takes the place of the more obviously appropriate bud 

 or fisssion-product. The phenomenon of Alternation of Genera- 

 tions, usually treated of in connection with parthenogenesis, 

 -should by experiment on the physical conditions accompanying 

 its variations enable us to ascertain a great deal more than is at 

 present known of what is the signification of the differentiation 

 of male and female sexual elements ; and it is from farther study 

 of this and of True I'arthenogenesis that progress in tliis part 

 of physiology may be expected. 



To return to Siebold's researches. The greater part of the 

 book is devoted to an account of the parthenogenesis observable 

 in the wasp Polistes. Leuckart first recorded in his work already 

 mentioned, that the workers of wasps, ants, hornets, and humble 

 bees lay eggs, which in one case he followed to the development 

 of a larva, but of which he was not able to determine the sex. 

 Siebold determined to study a species of Polistes common in 

 and around Munich, which he identities with much care, and 

 after reference to specimens and authorities from many lands, as 

 Polislcs galliia var. JiaJcDia Latreille. He gives a minute de- 

 scription of the characters of the females and males ; the two 

 kinds of the former (queens and workers) being only distinguish- 

 able by size — the workers in all external characters as well as in 

 their generative organs being merely smaller queens, and fully 

 capable of copulation and impregnation. In the beginning of 

 May, in Munich, the Polistes queens which were born in the pre- 

 vious summer and impregnated then, commence each to build a 

 nest. No queen who built in the former year survives to build a 

 second time, and the young queens never make use of the old 

 nests. The Polistes are very particular in choosing a warm sun- 

 shiny spot, sheltered from wind and rain, and as such spots are not 

 too common, a new nest is often begun near the weathered remains 

 of an old one. Walls and trunks of trees, often at such a heiglit 

 as not to be easily reached, are the sites chosen. When tlie 

 queen has constructed fifteen or twenty cells, she lays eggs in 

 them, and is very hard-worked in guarding her nest and in pro- 

 viding food for the larv.X' as they hatch. She feeds them on 

 caterpillars and other soft insects, first removing the alimentary 

 canal (as cooks take out the entrails of a fish), and carefully 

 applying the morsel to the lips of each larva. This process takes 

 some time for one "hand," and hence the first brood is longer 

 in coming to perfection than later broods, in the rearing of which 

 the elder progeny assist. In the middle of June the first lot 

 make their appearance, all small females ready to assist their 

 parent in the advancement of her enterprise. The later broods 

 develop more rapidly and acquire larger size from being better 

 nourished, and towards the end of June (no drones being as yet 



born) the females which come forth are as large as the old queen ; 

 they may, however, be easily distinguished from her by their 

 comparative freshness of colour and wing. Great care is dis- 

 jjlayed in guarding the nest. At night the queen goes to .sleep 

 after having carefully inspected each cell, taking up her ]iosition 

 at the hinder side of the nest. If she is disturbed in the night, 

 she takes another survey of her house before again going to sleep. 

 In the daytime if disturbed she makes an immediate attack on 

 the enemy with her sting, and then flies bick to her nest. .She 

 can sting several times, since the barbs on her weapon are not 

 too long to allow of its being withdrawn. Ants are amongst the 

 most common of the many insect enemies of these wasps, and 

 when one ventures into the nest, the whole colony sting it to 

 death, and immediately throw the body out. Birds are, how- 

 ever, not thus to be got rid of, and destroy immense numbers of 

 the nests, so that Siebold was obliged to protect those he wished 

 to study with nets. The members of one nest are not allowed 

 to remain in another, if by chance a stranger comes in she is 

 luBtled out at once by the wasps near the entrance. Siebold 

 convinced himself of this by painting the thorax of a number of 

 I'ulistes belonging lo different nests with different colours. Only 

 late in the year, when the wasps seem to be getting careless or 

 tired of their incessant work did he find that one or two had 

 got mixed in certain colonies, to which they did not rightly be- 

 long. Although there is this sharp discrimination of individuals, 

 yet it was found that by substituting one nest for another whilst 

 the queen was away, she could often be deceived, so as to make 

 her enter upon the possession of the substituted nest as though it 

 were her own. Siebold found this a very useful plan when he 

 wanted to change the position or locality of a nest so as to bring 

 it into a safer or more accessible spot, or when a nest which he 

 had been observing was by some accident deserted, or when a 

 nest in a favourable position was less forward in the develop- 

 ment of its larva; than one less favourably situated. By making 

 the nests moveable, and substituting the one for the other in the 

 absence of the queen, he was able to save himself much trouble 

 and li5ss. The nests were made moveable by removing them 

 from their original support and firmly fixing them to boards which 

 were then hung up in the original position. The queens were 

 very anxious after this operation had been performed, investigat- 

 ing with great care the strength of the supjiort and the cord by 

 which the .board was hung, and sometimes adding to it them- 

 selves additional strength. By degrees such moveable nests 

 could be lowered a little bit each day from an inconveniently 

 high position, or taking the nest in the night under a cover 

 whilst all the wasps were in it, it could lie removed from 

 a distant locality to the Professor's garden ; Jin such cases 

 a certain proportion always came to grief by the deser- 

 tion of the colony ; and the queen was then \ sometimes 

 found at work on the old site constructing a new nest. Al- 

 though strangers are not admitted in a well-regulated Polistes 

 nest, yet by carelessness or desertion the brood of one colony 

 will sometimes be exposed to the attacks of the workers of 

 another, who then make use of the unfortunate larva; to feed 

 their own young. It frequently happens that workers who have 

 once indulged in this kind of thing, become what are called 

 "robber wasps," utterly demoralised, and actually undo the 

 whole labour of a colony by dragging out the grubs which they 

 were lately so carefully tending in common with their fellows, to 

 feed the still younger larvoa. When this condition of things has 

 once begun in a colony it soon goes to ruin, and hence it is neces- 

 sary to destroy any deserted Polistes nests in the neighbourhood 

 of those under observation, lest by entering the former the mem- 

 bers of the latter should get the bad habit of pulling grubs out 

 of their cells, and proceed to do the same in their own nests. 



The rain is a very constant source of destruction to Polistes 

 colonies, drowning the young by saturating the cells with mois- 

 ture. Light rain will not, however, 'do much harm. Whilst Sie- 

 liold was endeavouring to remove some of the water from a nest 

 which had been drenched in a shower, he was astonished to find 

 the wasps themselves already busy at the work, putting their 

 heads into the cells, sucking up the water, then passing to the 

 edge of the nest and spitting out the fluid. In this way they are 

 able to get rid of the effects of a wetting if it is not very severe. 

 Though the Polistes feed their young exclusively with animal 

 food, they yet appear to collect a sweet fluid which .Siebold found 

 in some cells, and which he thinks the workers take for their 

 own enjoyment, since they were seen entering such cells and 

 apparently sucking at the contents — in fact, taking a little_ re- 

 freshment in the intervals of their labour. 



