226 



HAEDWICKE'S SCIENCE-GOSSIP. 



which "La fausse chenille du groselier" {Nemaha 

 ribesii) laid its eggs ; and in the case of the saw-fly of 

 the osier he sometimes found one layer of eggs on the 

 top of another, and both external to the plant. Vol. 

 v. pp, 128-9. "La coque de l'ceuf, son enveloppe, 

 est-elle une espece de placenta qui s'abreuve, qui 

 s'imbibe du sue de la partie de la plante sur laquelle 

 elle est posee, et d'un sue qui non seulement la 

 fait croitre, mais qui fournit a l'accroissement de 

 l'embrion qu'elle renferme ? Un oeuf qui a ete depose 

 dans la fente faite a. une tige de rosier, y est-il 

 greffe en quelque sorte ? Doit-il s'approprier le sue 

 de l'arbuste comme l'ceilleton d'un arbre, loge dans 

 la fente faite a l'ecorce d'un autre arbre s'approprie- 

 rait le sue de cet arbre? II semble que cela soit 

 ainsi." Then occurs to him the difficulty mentioned 

 above about the saw-flies of the currant and osier. 

 He adds: "J'ai fait une experience qui prouve 

 decisivement qu'il est essentiel a l'ceuf que cette 

 humidite lui soit fournie par la feuille." This was, 

 in brief, allowing some leaves with eggs on them to 

 dry up ; when the eggs perished, whilst those on 

 living leaves and on leaves kept fresh in water, 

 developed. He says : " Des ceufs de papillons qui 

 auraient ete laisses sur une feuille qui se serait 

 dessechee n'en auraient pas moins donne pour cela 

 des chenilles." That is, in ordinary circumstances, 

 because the eggs of Lepidoptera are better able to 

 retain their moisture. Finally, regarding the eggs 

 on the osier laid in a double layer, " ce qui semble 

 former une grande difficulte sur la maniere dont se 

 nourrissent les ceufs de la seconde couche . . . On 

 doit penser que l'humidite qui s'eleve de la feuille, 

 parvient a la seconde couche d'eeufs, ou que les ceufs 

 de la premiere couche fournissent a ceux de la 

 seconde ce qu'ils ont de trop d'humidite, et qui suffit 

 a ceux-ci." 



All this only demonstrates the necessity of 

 moisture for the development of the egg. An 

 experiment which I made last year shows in like 

 manner that moisture alone is sufficient, and that 

 no nutritive juice derived from the plant is in- 

 dispensable to this development. I succeeded in 

 hatching eggs of Zartxa fasciata and Nematus ribesii 

 on pieces of glass, away from the leaf altogether, 

 by simply keeping them always moistened with 

 plain water, in a covered vessel. All that is neces- 

 sary besides the interaction of the atmosphere is the 

 imbibition of water. And yet these eggs grow to at 

 least double their original bulk. The little mass of 

 protoplasm has within itself all other material 

 that is necessary to the building up of the em- 

 bryo ; and, sometimes at least, more than is 

 necessary or than can be used up in the process. 

 The matter which gives colour to the yellow yolk 

 of the egg of Gastrophysa raphani does not enter 

 into the composition of the larva. As the embryo 

 grows, the yolk, finally enclosed in the alimentary 

 canal, becomes deeper and deeper in colour, and 



the residuum is voided as an orange or reddish 

 meconium immediately after hatching, in excep- 

 tional cases even in the shell itself. 



When life, from being subaqueous, becomes sub- 

 aerial, various contrivances come into requisition for 

 the purpose of retaining within the organism, that 

 amount of free water which is necessary to the carry- 

 ing on of the processes of vitality. Since desiccation 

 suspends or destroys these processes, can we wonder 

 that an organism so minute and so passive, as an 

 insect ovum, should require not only special struc- 

 tures in its shell, but special conditions of the envi- 

 ronment to preserve it from a contingency so proxi- 

 mate and so fatal ? * The shell must not be totally 

 impervious, because the interaction of air and water 

 is necessary. Leuckart's description of the micro- 

 scopic structure of the shell shows how well it is 

 adapted to regulate this interaction within a given 

 range of hygrometric conditions. Many insects lay 

 their eggs in water, and such eggs have an almost 

 structureless chorion. For others the moist exhala- 

 tions from the leaves of plants are sufficient. Praso- 

 airis marginella cuts a hole in the hollow petiole of 

 Rammculus ficaria, and inserts her eggs in the tube 

 where they are always bathed in sap. Exposed to 

 the air these eggs would shrivel up in a day or two ;. 

 but they can be easily hatched in a covered saucer, 

 on a fresh leaf of any plant moistened with a few 

 drops of water. We have seen how, in two hymen- 

 opterous families, the same object is attained by 

 inserting the eggs in the tissues of plants. In the 

 case of the third mentioned family of Hymenoptera, 

 the ants, the due relation of the egg to the environ- 

 ment is the care of the workers ; and such is also the 

 plan adopted by the common earwig, according to 

 the account of Mr. Rennie in the " Penny Magazine." 

 He says : t "About the end of March I found an 

 earwig brooding over her eggs in a small cell scooped 

 out in a garden border ; and in order to observe her 

 proceedings I removed the eggs into my study, 

 placing them upon fresh earth under a bell-glass. 

 The careful mother soon scooped out a fresh cell, and 

 collected the scattered eggs with great care to the 

 little nest, placing herself over them — not so much, 

 as it afterward appeared, to keep them warm, as to 

 prevent the too rapid evaporation of their moisture. 

 When the earth began to dry up, she dug the cell 

 gradually deeper, till at length she got almost out of 

 view ; and whenever the interior became too dry, she 

 withdrew the eggs from the cell altogether, and placed 

 them round the rim of the glass, where some of the 

 evaporated moisture had condensed. Upon observing 

 this, I dropped some water into the abandoned cell, 

 and the mother soon afterwards replaced her eggs 

 there. When the water which had been dropped had 



* Possibly the layer of albumen in the bird's egg may sub- 

 serve a similar use. 



f I quote from a little book entitled "The Life of an Insect," 

 issued by the Society for Promoting Christian Knowledge. 



