Oct. 20, 1887] 



NA TURE 



593 



During the present summer it has been traced over the greater 

 part of England and Scotland, and the author found it on July 

 14 in fields of wheat and barley on the borders of South Wilts 

 and South Hants. The theory that the fly was introduced into 

 the United States Uy Hessian troops during the War of Inde- 

 pendence is regarded as untenable. Packard, discussing Wagner's 

 results, concludes that the Hessian fly had appeared in the 

 Eastern States before the Revolutionary War, that it has never 

 been known to inhabit England or Northern Europe, that it was 

 not known even in Germany before 1857, that it has •' from 

 time immemorial" been an inhabitant of wheat- fields on the 

 Mediterranean coasts, that it most likely originated in this 

 region, or farther east (in the probable original habitat of wheat 

 and other cereals), and that it was introduced thence into the 

 United States before the war. How it reached Britain is not 

 known, but it probably came as " flaxseeds " in straw used for 

 packing or for litter. Wheat, barley, and rye are the cereals 

 attacked ; oats appear to escape. The " flaxseeds " or puparia 

 have also been found upon timothy grass {Phlcum pratense, L.), 

 but there is no evidence of any other grass being attacked. 

 American observations indicate that the fly flourishes best in 

 warm, moist seasons, so that the hot, droughty character of the 

 recent summer can hardly have specially favoured it ; in fact, it 

 seems to have made headway under rather adverse conditions, 

 and with one of our usual moist summers the attack would 

 probably have been more severe. Many precautions have been 

 suggested for the use of agriculturists with the object of mini- 

 mizing the attacks in future years. Several species of Hymeno- 

 ptera are parasitic upon the Hessian fly. Specially useful in this 

 way are Semiotdlus destructor, Say, one of the Chalcididse, 

 which deposits its eggs in the pupa of the Hessian fly, and 

 Platygaster error, Fitch, which places its eggs within those of 

 the fly. These minute parasites have done splendid service in 

 the American wheat and barley fields, where they are as active 

 friends to the corn grower as are the aphis eating lady-birds in 

 this country to the hop grower. It has been suggested that if 

 the parasites have not accompanied the fly to Britain they 

 should be colonized here. On August 11, however, from a 

 ^"flaxseed" in the possession of the author there emerged a 

 ehalcis fly, and other observers have confirmed the presence in 

 this country of insect parasites of this much-dreaded crop 

 scourge. 



Recent Researches on Earthworms. — Mr. W. B. Benham 

 gave a general account of his own researches into the structure 

 of this group, as well as those of Beddard, Horst, Perrier, and 

 others. One object of the paper was to compare the facts 

 already known about this group and to deduce therefrom the 

 mutual affinities of the different genera. Perichate was regarded 

 as being an ancient form, while Criodriliis was' referred to as a 

 degenerate form. 



A Luminous Oligochmte. — Prof. Ilarker described a species of 

 Enchytraus which he had noticed gave off a brilliant phosphor- 

 escent light. 



Mr. F. E. Beddard communicated a paper On the Structure 

 of Fratercula arctica. The point of the paper was to record the 

 fact that the "oblique septa" of this bird, like those of the 

 duck, were covered with a layer of muscular fibres ; in this 

 respect these two birds agree more closely than any other birds 

 with the crocodile, in which animal, according to Prof Huxley, 

 the homologues of the oblique septa are largely muscular. 



On Cramer's Gemma borne by Trichomanes alata. — Prof. 

 Bower described peculiar developments on a plant of Tricho- 

 manes alata from the Royal Botanic Garden in Edinburgh. 

 From the tips of the pinnje are produced flattened outgrowths of 

 an apparently prothalloid character ; these produce spindle- 

 formed gemmse, which are recognized as corresponding to those 

 previously described by Cramer. These are thus shown to be 

 genetically connected with a plant of Trichomanes, and the 

 opinion of Cramer is thus now confirmed ; but, further, if the 

 flattened outgrowth on which they are produced be truly pro- 

 thalloid in its character, there is here a further example of that 

 direct transition from the fern plant to the prolhallus which has 

 been described under the name of apospory. 



On Benncttites, the Type of a Ne^u Group between Angio- 

 spcrms and Gymnosperms. — Count Solms-Laubach described a 

 genus of fossil plants, Bennettites, the type of a new group 

 between Angiosperms and Gymnosperms. The plants in ques- 



tion accord with the Cycadeae in their vegetative structure, but 

 possess fruits which exhibit the true structure of the Gymno- 

 sperms. 



The Secretion of Pure Aqueous Formic Acid by Lepidopter- 

 ous LarvcB for the Purposes of Defence, by E. B. Poulton.— 

 It has long been known that the larvae of the genus Cerura 

 (Dicranura) have the power of ejecting a colourless fluid from 

 the mouth of a gland which opens on the prothoracic segment. 

 The latter segment is dilated when the larva is irritated, so that 

 the fluid is thrown in' a forward direction, and for a distance 

 of several inches. When the larva is touched, the head and 

 anterior part are immediately turned towards the source of irri- 

 tation, and the fluid is thrown in this direction. In 1885 I 

 found that the secretion was strongly acid to test-paper, and that 

 it caused very strong effervescence when placed upon .sodium 

 bicarbonate ; while a little later I showed the fluid to Prof. 

 Wyndham Dunstan, who told me that the characteristic smell 

 of formic acid could be plainly detected. This opinion was 

 further confirmed when it was found that silver nitrate was 

 readily reduced by the secretion (Trans. Ent. Soc. Lond. 1886, 

 part ii., June, pp. 156-57). In 1886 I obtained a larger num- 

 ber of larvae, and with the kind help of Mr. J. P. Laws, I was 

 enabled to show that the secretion contains about 33 per cent, of 

 anhydrous acid. All the well-known qualitative tests were applied 

 to the secretion and to the alkaline salts obtained by neutraliz- 

 ing with standard alkali. Among other tests, the secretion was 

 found to dissolve the oxide of lead, a white crystalline salt being 

 deposited. Although only a very minute weight of this was 

 obtained. Prof. Meldola kindly offered to estimate the amount 

 of lead present in the salt. The weight was found to correspond 

 to one of the basic formates of this metal formed by the action 

 of the normal formate upon the excess of oxide. During the 

 past summer I have had a very large number of these larvae, 

 and the investigation has been continued with larger amounts of 

 secretion. The pipette has been applied for the removal of 

 secretion between 500 and 600 times, and between twenty and 

 thirty volumetric determinations have been made. A mature 

 larva which has not been previously irritated will eject '050 

 gramme of secretion containing about 40 per cent, of anhydrous 

 acid . Half-grown larvae eject nearly as much, but the fluid is 

 weaker, containing about 33-35 per cent, of acid. The rate of 

 secretion is comparatively slow — e.g. two days and a half after 

 ejection, two large larvae only yielded together "025 gramme of 

 secretion. Two captured larvae, to which the eggs of para-itic 

 Ichneumonidse had been affixed, only ejected '035 and '045 

 gramme of secretion ; having incompletely made up the amount 

 losi during the attack of the Hymenopterous insect. Starvation 

 lessens the amount of secretion, and also decreases the propor- 

 tion of acid ; but probably both these effects are due to general 

 health, and do not imply the direct formation of the acid from 

 the food. The different food-plants — poplar and willow — do 

 not make any difference in the amount or strength of the secre- 

 tion. About half the total quantity of secretion obtained was 

 made use of in preparing a relatively large amount of the nor- 

 mal formate, which is now in Prof. Meldola's possession. The 

 weights of the constituent elements will be determined by com- 

 bustion. The rest of the secretion has been used for other exact 

 methods of estimation and analysis under the kind direction of 

 Mr. A. G. Vernon Harcourt, the work having been conducted ' 

 in his laboratory at Christ Church. Mr. Harcourt suggested 

 that it was most important to prove that the amount of acid 

 shown to be present by volumetric analysis is formic acid, and 

 nothing else. This proof was obtained in two ways : (i) a 

 certain weight of the secretion was divided into two parts ; 

 the amount of acid in one of these was determined by the volu- 

 metric method, while the other was decomposed by strong sul- 

 phuric acid, and the carbon monoxide which was evolved was- 

 exactly measured in the apparatus for gas-analysis, and the 

 amount of formic acid present was calculated from the data thus 

 obtained. The two percentages nearly corresponded, and, as 

 the latter was the higher, it was obvious that no other acid 

 could be present. (2) A certain weight ("186 gramme) of 

 secretion was heated in a tube over a water bath, and, after 

 drying at iOD°C., only •cxx)4 gramme of solid residue remained, 

 and this was probably accidental. The rest of the fluid was 

 distilled into a tube containing carbonate of lead, ami this was 

 afterwards heated to 100° C, and the water collected in drying- 

 tubes. As a result, the increase in weight of the latter, and 

 the tube containing lead carbonate, the weight of formate of lead 

 obtained from the latter, and of sulphate of lead obtained from the 



