HARDWICKE'S SCIENCE-GOSSIP. 



225 



detached. Can feeding under such conditions be free 

 from pain ? Judging from my own experience of a 

 loose tooth I should say decidedly, No ; but when we 

 remember that the nettle forms the diet of some 

 species of snails, we should feel disposed to modify 

 our views of the question. 



A strong muscular attachment connects the second 

 portion of the buccal apparatus with the jaw ; this 

 consists of a crescentic shape chitinous plate striated 

 where the laminae show the thickening of the organ. 

 Some are folded and thickened into bold transverse 

 ridges, while others are nearly quite destitute. As 

 Mr. Crowther, in his admirable paper in Science- 

 Gossip for January, has entered fully into this part 

 of the subject, I will merely say that what he has 

 written about snails I have found to hold good about 

 slugs. In the case of the latter, however, I have 

 not found the immersion in hydrochloric or acetic 

 .acid to have any appreciable effect on the denticles. 



I have found the following an easy method of ob- 

 taining these organisms. Remove by partial dissection 

 the buccal mass, soak in caustic potash for some time, 

 -or boil, if greater expedition is required ; partly 

 fill the test-tube with water, and shake briskly ; 

 the tongue and jaw connected will separate from 

 the surrounding mass, and can be readily discovered 

 and removed for further treatment. I generally mount 

 in Canada balsam, and since I became acquainted 

 with the wet process, I have had no difficulty in 

 making very creditable slides of animal substances. 

 I therefore recommend a perusal of the article by 

 Mr. Underhill, published in Science-Gossip in 

 May and June 1879, to whom I am indebted for 

 the process, and I shall be glad if you will allow me 

 to thank him for the very useful information. 



By this method I have been able to obtain the 



odontophore and jaw of that minute creature Vertigo 



£iie>itnla, which is a fairly good test of the process. 



W. H. Harris. 

 Cardiff. 



ON GROWTH IN THE EGGS OF INSECTS. 

 By Dr. J. A. Osborne. 



THE phenomenon of increase of bulk taking 

 place in the ova of some insects, after they 

 have been separated from the body of the parent, 

 has excited a good deal of interest ever since its 

 discovery. In the third volume of Kirby and 

 Spence's " Entomology," p. 91 seq., we read, — 

 " Another peculiarity ... is ihe augmentation in 

 bulk which takes place, after exclusion, in the eggs 

 of the great tribe of sawflies, the gall-flies, the ants 

 and the water-mites. Those of the two former, 

 which are usually deposited in the parenchymous 

 substance of the leaves, or of the young twigs of 

 various plants, imbibe nutriment in some unknown 

 manner, through their membranous skins, from the 



vegetable juices which surround them, and when 

 they have attained their full size are nearly twice as 

 large as when first laid. Except in the eggs of fishes, 

 whose volume in like manner is said to augment 

 previously to the extrusion of the young, there is 

 nothing analogous to this singular fact in any other 

 of the oviparous tribes of animals, the eggs of which 

 have always attained their full size when they are 

 laid. It is to M. P. Huber that we are indebted 

 for the knowledge of the fact that the eggs of ants 

 grow after being laid, a circumstance favoured 

 probably by the moist situation in which the workers 

 are always careful to keep them. By an accurate 

 admeasurement he found that those nearly ready to 

 be hatched were almost twice as big as those just 

 laid . . . Dr. Derham seems to have observed, that 

 the eggs of some Diptera, of the tribe of Tipulariae, 

 also increase in size before the larva is excluded. It 

 seems to me likely enough, that in this and many of 

 the above cases in which the egg is supposed to grow, 

 it is rather an extension of the flexile membrane that 

 forms their exterior proportioned to the growth of 

 the included embryo from food it finds within the 

 egg, than from any absorption from without." In 

 the number of the " Entomologist's Monthly Maga- 

 zine " for Sept. 1882 (pp. 77-78), Mr. W. Buckler, 

 writing of the eggs of a moth, Ennychia anguinalis, 

 states that "though they were very flat when first 

 laid, as Mr. Jeffrey informed me, yet I found they 

 had begun to swell and by the next day had filled 

 out considerably." Again, "The egg of anguinalis 

 is round and flattened, becoming more and more 

 convex and plump above as the embryo develops." 

 In rearing from the egg last year the larvae of 

 Adimonia caprea: (a beetle of the family Gale- 

 rucidce), I had frequent occasion to observe a 

 similar filling-out of the eggs, which when laid 

 were variously flattened and indented, but gradually 

 became full, plump and spherical. It seemed to 

 me also that they attained a size which must have 

 involved some stretching of the chorion. In these 

 two latter cases, the increase of bulk, though to a 

 smaller extent, is not less real a phenomenon and 

 equally demands an explanation, as in the more 

 striking instances of the saw-fly and Cynips. What 

 in the nature of this process ? Are these eggs able to 

 absorb and assimilate nutritive matter in the same 

 way as the larva does ? This seems to be the opinion 

 hinted at by K. & S. Westwood repeats their words 

 (Mod. Class ii. p. 96) ; and both are simply reiterating 

 the hypothesis of Reaumur.* He says (" Memoires," 

 vol. v. 179) : " Les ceufs de certaines mouches ont 

 besoin d'etre humectes, et meme nourris . . . par la 

 scve que fournit la branche dans laquelle ils ont ete 

 loges.' But Reaumur was by no means sure of the 

 matter. He could discover no incision in the leaf on 



* Or perhaps of Vallisnieri, the first to observe and describe 

 these things in the saw-riy. 



