HA RD WICKE' S SCIENCE- G O SSI P. 



235 



'by the lime salts of the cement combines with 

 aluminate of lime to give a double crystalline salt 

 containing half its weight of water. The crystallisa- 

 tion of a salt so full of water— or so " hydrated," to 

 use the chemical term — involves considerable swelling, 

 •which accounts for the breaking up of cements in 

 marine work, such as piers, breakwaters, and the 

 like. 



A very suggestive paper has just been published by 

 Mr. James Weir (read before the Institute of Marine 

 Engineers) entitled "Steam Engine Efficiency: a 

 comparison of Nature's Engine and Modern Prac- 

 tice." 



ZOOLOGY. 



On the Burrowing Habits of the Genus 

 Testacella (Cuvier).— Respecting Mr. Horsman's 

 remarks on my paper published last March in the 

 "Naturalist," "On the Burrowing Habits of Certain 

 Land and Freshwater Mollusca," it appears very 

 evident to me that his conclusions were drawn from 

 insufficient observations. Mr. Horsman informs me 

 that his observations extended over a period of five 

 or six months, and were carried out under artificial 

 •conditions. Under these circumstances, it is hardly 

 fair, I think, to criticise observations made from 

 nature. " A fairly heavy soil " kept in a " large old 

 4ank in an outhouse " would soon become caked and 

 very firm, and consequently it would be almost 

 impossible for a mollusc to get below twelve inches, 

 in fact I do not contend that in heavy soils molluscs 

 do burrowlto great depth. Where I saw T. halio- 

 iidca, it was in a light loamy soil. Mr. Horsman 

 speaks of the average depth as five or six inches ; now 

 liad he paid the slightest attention to the habits of 

 ■our British slugs in their natural conditions he would 

 know that most of them burrow to that depth when 

 •depositing their eggs, as has been described by 

 Moquin Tandon; and other writers. I have not had 

 the opportunity of studying T. scutulum, but from 

 what I know of ;the habits of T. haliotidea, I cannot 

 see any valid reason to doubt the accuracy of Mr. 

 Quilter's observations, nor do I agree that Dr. 

 Jefi"rey's statement is open to question. The other 

 records mentioned in my paper are all from well- 

 known conchologists and careful observers, and I 

 fail to see any cause for doubting them. — W. E. 

 jCoUi7ige. 



Early Butterflies.— Mr. Lowe, a short time 

 ago, stated that on the 3rd of June, he took a freshly 

 emerged specimen of C. edusa, and he asked whether 

 that is not very early for its appearance. If he 

 thinks it was freshly emerged simply because it was 

 fresh-looking, I think he may be mistaken, for as a 

 rule edusa hybernates as an imago, though Newman 



does speak of one that, contrary to the habit of the 

 species, passed the winter as a chrysalis. I say 

 I think Mr. Lowe may have been mistaken, for on 

 referring to my note-book for the current year, I see 

 it was on the 8th of June that I saw the first speci- 

 mens of P\ cardiii, an insect which also hybernates in 

 the perfect state, and I find I made the following 

 note, " Saw four or five V. cardui, all looked remark- 

 ably fresh and as if just out of the chrysalis." I have 

 no reason, however, to suppose that these butterflies 

 did not — as the species does — hybernate as imagos, 

 nor do I think it likely that Mr. Lowe's edusa had 

 not followed the usual habit of that species. Cardui 

 and atalanta were very numerous here this year, 

 especially in the larval condition. I found the 

 former feeding on both the common nettles, also on 

 Carduus arvensis^ C. pycnocephaluSy but I think it 

 seemed to prefer the small nettle ( U. urens) to any 

 other food. Curiously enough I took one half-grown 

 larva off the common mallow and reared it solely on 

 that. It preferred blossoms to leaves and would not 

 eat the latter when flowers were to be had. As I 

 am on the subject of butterflies, I may mention that 

 C. edusa has been scarce hereabouts this autumn. I 

 have traversed the Downs in all directions almost 

 daily since the beginning of September, and during 

 my excursions I have visited most of the clover-fields 

 within several miles of this place, the result being 

 that I found this insect plentiful at only one spot. 

 This was a small clover-field of about six acres, near 

 the lighthouse W. of Beachy Head. Some six or 

 eight visits to this resulted in my securing about 120. 

 Twenty-two of these were females, the rest males. 

 Of the former two were very fine examples of the 

 variety Helice. Early in the month they were in 

 very fine condition except that about one in six had 

 a large notch in one or two of its wings. At first I 

 could not account for this, but I soon discovered that 

 the injuries were caused by wheatears, which fre- 

 quented the field, and which poised on the top of a 

 stalk of clover, or hovering kestrel-like about a foot 

 above the level of the field, kept a sharp look-out for 

 passing butterflies, and whenever edusa came near 

 enough the bird darted at it like an arrow, and 

 though I never saw any butterflies secured I could 

 see plainly that that was how they got so damaged. 

 On one occasion, the insect when attacked mounted 

 like a heron pursued by a peregrine. It was most 

 interesting to note the extremely rapid movements of 

 ediisa as if fled from and dodged its pursuer with a 

 celerity that was marvellous. When they had 

 mounted until they were almost invisible the bird 

 suddenly relinquished the chase, and dropping 

 quickly to the ground was instantly followed by the 

 butterfly, which immediately resumed its rapid quest- 

 ing flight over the clover, just as if nothing had 

 happened. I will only add one more note. About 

 three weeks ago a very fine healthy caterpillar 

 of D. gain (found on the Downs) was brought to 



