246 Benj. D. "Walsh on the Insects inhabiting the Gulls 



It has been shown, I think, that the bullae cannot be caused by the 

 folds of the wing, as Jurine imagined, in any other sense than that in 

 which the teeth of a Mammal may be said to be caused by the gums. 

 Neither can we accept the other hypothesis broached by this author, 

 namely, that the bullae are connected with the respiratory system, be- 

 cause the wing-veins are now generally supposed to be, not tracheae or 

 air-conducting tubes, as he imagined, but true veins or blood-conduct- 

 ino- tubes. But may it not be possible that the bullae and the bullar 

 streaks are connected with the circulatory system ? Until microsco- 

 pists are agreed on first principles, it is difficult to answer this question 

 satisfactorily. On the one hand, Bowerbank and others, according to 

 Westwood, have proved " the circulation of a cold, transparent, and 

 nearly colorless fluid, not only in the larvae of Ephemera, Sec, but also 

 in the reins of the wings of the perfect Hemerohius." (Introd. I, pp. 

 11 and 15.) On the other hand, according to our distinguished 

 American microscopist, Prof. H. J. Clark, the blood, as seems to be 

 inferred from his language, circulates in the wings of insects, not 

 through what are usually called the veins, but through channels which 

 have no determinate walls. "A careful examination," says this last 

 author, "of some of the more transparent insects, such as the May-fly, 

 (Ephemera^) Gall-fly, (Ci/nips,) Plant-louse, (Ajyhis.) Lace-winged 

 Fly, (^Chrysopa^) Dragon-fly, (jEschna, Agrion, Libellula,) and the 

 grub or worm of many more, has convinced me that, notwithstanding 

 the apparent lack of w alls to the channels of circulation, the course of 

 the blood is none the less definite; always passing in one set of 

 channels going from the heart, and returning toward it in another set. 

 This is particularly noticeable in the head, legs and wings." (Mind in 

 Nature, p. 224.) There are three facts, however, which induce me to 

 think, that the bullar streaks cannot perform the same function as the 

 veins in Vertebrata, i. e. reconducting to the heart the blood distri- 

 buted by the arteries, on the assumption that the wing-veins act as ar- 

 teries, or vice versa. 1st. As may be sceu in Fig. 1, they cross the 

 wing veins in all directions. 'Ind. As is also shown in Fig. 1, and as 

 any one may easily satisfy himself to be really the case, by inspecting 

 the natural wing, instead of the branching bullar streaks thickening 

 as they unite with each other and approach the heart, they positively 

 become slenderer, aud sometimes even become subobsolete, as they ap- 

 proach either the costa or the base of the wing. 3rd. In the geuup 

 Dolerus (= Dosytheus) in 27 specimens of 8 species that I have exam- 

 ined, all of them with distinct bullar streaks, (including sericeus Say, 



