Insects. 



7885 



the abdomen were not dotted. On a careful examination with a microscope, which I 

 took into the garden, the thread appeared only slightly thicker than an ungummed 

 line, but after a very short time undulations appeared, and subsequently, at the most 

 regular distances, the viscid matter formed into alternating large and small globules. 

 The whole process is such a beautiful illustration of molecular attraction, which Mr. 

 Rainey has been so patiently and profoundly working out with regard to the highest 

 organic structures, that I thought this simple example might interest some of our 

 members. The cold weather has, of course, driven away this spider till next autumn 

 at least, but the same result can easily be obtained artificially. — Richard Beck y in 

 1 Journal of Microscopical Science.'' 



Mangold Wurzel Crops injured by a Species of Anthomyia. — With a view to ascer- 

 tain the origin of the evil, I paid frequent visits to a mangold field, in order to 

 discover the fly which was the parent of the leaf- mining larvae whose existence within 

 the cuticles an intelligent farmer had first pointed ont to me. I searched hundreds of 

 leaves, in order to obtain possession of some pupa?, but in vain. I brought home 

 several leaves containing full-grown larvae, which I anticipated would soon become 

 pupae, and placed them in water, in hopes of thus being able to secure a pupa or two ; 

 but I found the larvae always dropped out of the leaves. Failing in this, I determined 

 to watch the insects in the field, and my suspicions were soon fixed upon a two-winged 

 fly with reddish brown eyes, which was very abundant on the mangold leaves, and 

 seemed evidently to have some object in view beyond the mere ordinary and incidental 

 one of settling upon them. I observed, on the under surface of the leaves, a number of 

 small white cylindrical ova, in clusters varying from two to six or eight together. On 

 holding these up to the light I could clearly see from the track, which extended from 

 the ruptured ova between the cuticles to the larvae in another part of the leaf, that 

 these were the undoubted ova of the damaging insect; but it still remained to 

 prove that the suspected fly was the parent of the ova. I therefore made a micro- 

 scopical examination of the eggs which had been deposited on the leaves ; these, under 

 a power of 250 diameters, presented a beautiful reticulated structure. I then dissected 

 a number of the flies, whose abdomens were evidently distended with ova, with a view 

 to compare the eggs in the ovary with those I had already examined. I found them 

 in every stage of development, and discovered some of the exact shape and size, though 

 of softer consistency than the eggs on the leaves, aud presenting the same network 

 structure, characteristic of those which had been naturally excluded. About this time 

 I was made acquainted with Mr. Curtis's description of the male Anthomyia Betae, 

 which exactly agreed with specimens I had taken myself, and as I afterwards discovered 

 a couple of flies in coitu I could no longer have any doubt on the subject. It appears 

 singular that this is the first instance on record of the mangolds suffering to any extent 

 from the depredations of these larvae, the direct cause of the injury last year being the 

 large proportion of female flies compared with the number of the males, being on an 

 average as twelve to one: from the fact of the males only being hitherto recognised, 

 there can be little doubt that in former years this sex predominated, hence the immu- 

 nity of the plants from injury up to this time; but, as to the cause, whether atmo- 

 spheric or otherwise, of the large proportion of females during the last year, this is a 

 question which perhaps can never be solved. The female fly continues to deposit ova 

 quite late in the season ; I found this to be the case as late as the first week in 

 November. I cannot think that the larvae change to pupa? in situ; I never could 

 detect a single pupa in the leaf, and my observations, so far as they go, tend rather to 



