272 



HARDWICKE'S SCIENCE-GOSSIP. 



shows the presence of the delicate species just men- 

 tioned, we must act in the following manner : — 



(b) Slow Method. — The diatoms are slightly heated 

 (by the sun or on a hot stove) with some hydrochloric 

 acid, to which we add little by little small crystals of 

 chlorate of potassium. The chlorine is left to operate 

 for some days (being frequently stirred), until the 

 diatoms are bleached white at the bottom. 



If the endochrome is not entirely destroyed, it must 

 be removed by decanting the acid liquid and allowing 

 aqueous caustic ammonia (volatile alkali) to act on it 

 for one or two days. This alkali is decanted, then 

 we allow several days to intervene, during which cold 

 concentrate nitric acid is operating. (The action of 

 the alkali in juxtaposition to the acid operates through 

 the silica of the valves by endosmose, and this internal 

 current completely destroys the endochrome and the 

 coleoderme.) Washing and drying follow as in 

 Method a. I recommend this method ; it is slow, 

 but it is excellent, and when followed exactly it gives 

 a remarkably beautiful preparation. 



(e) Type Preparations.— When the diatoms have 

 been well washed and dried on the slide, the most 

 beautiful examples may be picked out and chosen in 

 order to make preparations containing only one type 

 species. This is done with a prism, having a power 

 of + 100 or 150, and with a hair from a brush, which 

 serves to detach them and transport them one by one 

 on to the cover, in the centre of a small circle, pre- 

 viously necessary, drawn with red, blue, or black 

 varnish. This circle can be easily made, and it 

 enables us to find the objects rapidly. The slide 

 should be previously covered with a thin film of 

 glycerine, which serves to fix the diatoms when 

 placed upon it. A gentle heat afterwards volati- 

 lises this glycerine. The preparations thus made are 

 clean and very useful, but they require much time 

 and skill. 



Translated by W. Bate Hardy. 



THE ROSE CUTTING BEE {MEGACHILE 

 IVILLO UGHB1ELLA) . 



THE constructive instinct of insects is apparently 

 developed to its greatest perfection in the order 

 Hymenoptera, more especially among the sociable 

 species. Yet there are some solitary individuals that 

 approach, if they do not equal, them in this respect. 

 And among the latter none more so than the leaf 

 rollers. 



I observed one of these solitary species of bees 

 [Megachile Willoughbiella') constructing a domicile for 

 its progeny in the loose earth of a flower-pot, though 

 the soft wood of a decayed post, or the crevice in an 

 old wall is frequently selected by it for the same 

 purpose. If it chooses a flower-pot it burrows a 

 cylindrical hole about half an inch in diameter ; 

 tunneling with its powerful jaws, it tears down small 



particles of earth which it rakes to the surface by 

 means of its feet, for which purpose they are admirably 

 adapted, but as it accumulates the earth from within 

 at the entrance, it from time to time levels the suc- 

 cessive heaps to a uniform surface. This tunnel 

 which occupies the persevering toiler about two days- 

 to form, is from three to four inches in length, some- 

 times it is a straight or curved cylinder, and sometimes 

 it is branched or bifurcated, but in all cases it is 



Fig. 158. — Megachile Willoughbiella cutting a piece of leaf 

 for wall of cell. 



smoothly finished inside. It may happen that 

 another bee of the same species will select the same 

 flower-pot in which to construct its nest, but each 

 works independently of the other. Should a wooden 

 post be selected for its nest the bee will carry the 

 extracted particles some few inches away, and scatter 

 them about, evidently not caring to accumulate 



Fig. 159. — The leaf of a Rose cut by Megachile Willoughbiella. 

 a, A piece cut for the wall of a cell ; b, A piece cut for roof 

 of" a cell ; c, Section of b, showing the turned up cd^e ; 

 d, Defective cutting. 



rubbish that would be liable to betray its sequestered 

 home. 



Again, the crevice in a wall may be chosen, then it 

 has little else to do than to clear the loose material 

 away and construct its cells. Having completed the 

 boring operations or adapted a ready-formed burrow 

 as the case may be, it sallies forth to some bush, that 

 of the "tree peony" or " rose " (from which it 

 derives its name) or some other suitable plant. 



