114 HALF-AN-HOUR 



Acari from Linnet's Nest (PI. XIV., Figs, i — 5) are probably 

 examples oi Der77ia7iyssus aviu?n, an acarine parasite found in the 

 cages of tame singing birds, of which I have for long been in 

 quest of living specimens. Some time ago I purchased a slide 

 of " Bird-mites^'' which shall be sent round for comparison whilst 

 the memory of the present one is still fresh. The mandibles of 

 mine are chelate ; whether they are so here I cannot feel quite 

 sure. Chloride of calcium is the preferable medium for mounting 

 Acari, so that the minute details of structure may be precisely 

 made out. The mandibles of the male D. avium are said to have 

 " a long external claw " ; those of the female to be ensiform. 

 They appear to be truly sword-like in a larger species, D. galli?ice, 

 not uncommon in poultry houses, and which I have had the 

 opportunity of dissecting. 



Eggs of Lace Wing Fly (PL XIIL, Figs. 3— 8).— This slide 

 shows close observation of nature, and careful endeavour to pre- 

 serve phases in a curious and instructive life-history. These 

 qualities I trust to see more and more of with our members. It 

 is not by purchased slides, ready prepared, that insight is best 

 gained into the ever-fresh wonders and beauties of Nature, but by 

 carefully observing and truthfully recording what we see. The 

 specimens tell this tale so well that it will be unnecessary here to 

 dilate upon it. 



Dr. M has asked, " How is the stalk formed ? " We 



learn from " Lowne on the Blow-fly '' that in that insect there is, 

 at the anterior extremity of the common oviduct, a pouch. Into 

 this pouch the orifices of the albumen glands and of the receptacle 

 seminis open, and that it appears probable that as the eggs pass 

 through this pouch they are fertilised, and immediately covered 

 with a sort of varnish secreted by the albumen glands. (For 

 diagrammatic sketch see PI. XIIL, Fig. 7.) 



Now, if we suppose the eggs in the " Lace Wing Fly " to be 

 covered with a somewhat larger quantity of albuminous material, 

 that shall be rather longer before it finally dries, we shall have the 

 required conditions, as in a, b, c, d, Fig. 8 (same plate), where a may 

 be taken to represent the egg at its first protrusion, coated with a 

 viscid fluid, indicated by the dotted line ; b, c, the same, still in 

 the grasp of the ovipositor, but adhering to the object on which it 

 has been deposited, and so being drawn out. At d, the thread 

 having attained its full length, the parent insect has left it to 

 repeat the operation. I should expect to find an account in 

 either Swammerdam's ^'- Biblia Natiirce^'' or in the works of 

 Reaumer or De Geer. The subject is deserving of investigation 

 in the light that may be thrown on it by our modern 

 microscopists. 



