HABDWICKE'S SCIENCE-GOSSIP. 



147 



the mauna collected on the sixth day " did uot 

 stink " on the Sabbatb, although it did so on the 

 other days if kept over the day, is removed by the 

 direction of Exodus xvi. 23, " Bake that which ye 

 will bake to-day, and seethe that ye will seethe " ; in 

 other words, by scalding, clearly directing and show- 

 ing how decomposition was to be avoided, adding, 

 " that which remaineth over lay up for you to be 

 kept until the morning." It is probable that the 

 lichen with which the Israelites were fed was the 

 affinis, which is so closely allied to the esculenta, that 

 Lindley treats them as almost the same, and as tra- 

 versing the same regions. There may, however, be 

 a slight difference in the taste and colour between 

 the plants of the East and the plants of Algiers, 

 which Lindley calls a " species or variety " ; indeed 

 the Mosaic account itself varies as to the taste, for 

 in Exodus xvi. 31 it is said to be "like wafers 

 made with honey" whereas in Numbers xi. 8 it is 

 said that " the taste of it was as the taste of fresh 

 oil." 



The enormous additional quantity requisite for 

 the subsistence of the Israelites, as stated on calcu- 

 lation, in the "Dictionary of the Bible" (viz. 

 15,000,000 lb. a week), might of course be raised 

 as far as necessary, by Divine agency increasing 

 the growth of the plant without depriving it of its 

 character as a natural product. 



I have conversed with several clerical friends who 

 have read the above-mentioned articles, and who are 

 satisfied with the proofs adduced ; indeed, they 

 first drew my attention to Exodus xvi. 23, as to 

 the preservation of the manna over the sixth day by 

 scalding. 



Lindley gives illustrations, in his " Vegetable 

 Kingdom," of the two Eastern plants, L. escule?ita 

 and L. affinis. The L. esculeuta of Algiers, which 

 Lindley calls a species or variety, is illustrated in 

 Science-Gossip for March, 1872. 



Brighton. T. B. W. 



NOTES ON THE DIPTERA. 



{Continued). 



June to August :— Gad-flies. 



AMONG the many flies which haunt the banks 

 of streams and ponds, fields where cattle are 

 grazing, woods, and similar places, there are none 

 more likely to attract attention than the Tabanidae— 

 Gad-flies, Breeze- flies, or Brown-stouts, as they are 

 sometimes called. They are well known to farmers, 

 and indeed most people who frequent the country 

 are more or less acquainted with them. 



Their general shape, when viewed from above, 

 is somewhat oval. The head is wider than the 

 shoulders or prothorax, but not so wide as the 

 middle portions of the insect. Their eyes are gene- 

 rally brilliantly coloured, and possess a metallic 



lustre. They are moderately strong insects, but 

 their bodies are soft, not having so horny a covering 

 as some of the other diptera, such as the Muscidae. 

 They are covered with short fine hair. 



The food of the males, in the imago state, is the 

 nectar of flowers ; but the females, although we 

 believe that they also eat honey, feed on the blood 

 of cattle, horses, and even men, whose skin they 

 pierce by means of their elaborately constructed 

 mouths. 



The males of the Tabanidae are far less frequent 

 than the females. They may be recognized by their 

 two eyes touching each other, instead of being, as 

 in the female, far apart : the upper halves generally 

 have larger lenses than the lower, and are furnished 

 with a hair at each angle of the lenses, while the 

 lower halves have no hair. The mouths of the 

 males have no mandibles (md, fig. 96), and conse- 

 quently are not adapted for piercing the skin ol 

 animals. 



According to Walker's classification, the Taba- 

 nidee are the third family of the Brachycera, and 

 there are three British genera, viz., — Tabanus, 

 Hcematopota, and Chrysops. Individuals of the first- 

 named are plentiful (too plentiful, in fact) in hot 

 countries ; but although the species are numerous, 

 they are comparatively rare in England ; and there- 

 fore our intention is to notice, not so much the 

 genus Tabanus, as the much commoner genera 

 Haematopota and Chrysops. We will therefore dis- 

 miss the Tabani with noticing by what features they 

 may be known when found. 



On comparing the three antennae (fig. 93, a, b, and 

 c), it will be seen that that of Tabanus luridus has 

 a tooth or projection at * : this tooth is present in 

 the genus Tabanus only. The wings, also, of this 

 genus are almost colourless, thereby differing from 

 those of the other genera as described below. We 

 have given a figure of the wing of Tabanus rusticus 

 (fig. 91) as a type of the wings of the Tabanidae. 



T. bovinus is the largest of our native diptera ; it 

 is one inch long, including antennae, and is also very 

 broad and thick. 



ELematopota. — Perhaps there is no entomologist 

 who has not been troubled, when hunting insects in 

 the summer, by a grey fly with a large head, bright 

 eyes, and grey wings folded over the back when at 

 rest. It has a rather peculiar appearance, and non- 

 entomological friends, when they see it, are apt to 

 exclaim, " Oh, what a curious moth ! " It flies 

 slowly round and round one's head with a deep but 

 indistinct hum, and not only pierces the face and 

 hands with its sharp lancets, i.but has a ridiculous 

 habit of poking its tongue into the seams of one's 

 coat as if it would extract nutriment therefrom. This 

 fly is Hamatopota phivialis. It is the commonest 

 of the Tabanidae, and it may be found in abundance 

 in fields where animals are grazing, and in most 

 places not far from water. Its size is variable, but it 



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