JOURNAL OF THE ROYAL MICROSCOPICAL SOCIETY. AUGUST, 1908. TRANSACTIONS OF THE SOCIETY. XI.-On the Microscop as an Aid to the fltudy of Biology in Entomology, with particular reference to the Food of Insects. By W. WESCHE,F.R.M.S. (Read January 15, 1908.) PLATESV. TO X. ENTOMOLOGISTSare generally satisfied with the identification and classification of their specimens ; connected with this work are many points of the greatest interest, such as variation and mimicry, and in the phylogeny new points are constantly arising and give little leisure for other work. So the large majority of the life-histories still remain unstudied, and the habits of many well known species _-- -I__- EXPLANATION OF PLATE V. Fig. 1.-Fore leg of Chrysops cecutiens L. 0. To illustrate the simple type of limb. This insect belongs to the family of the Tabanids, and is a well known and keen blood-sucker. It is mot with in our English woods and meadows. Fig. 2.-Middle leg of Chrysopilus aureus Mg. 0. Simple type. Belongs to the Leptids, and is not uncommon in long grass and meadows. Fig. 3.-Hind leg of Beris vallata Forst. 0. Simple type. Belongs to the Stratiomyidse ; is very common, and found on the hedges. Fig. 4.-Fore leg of Hydrophorus ; species undetermined ( 8 ). To illustrate the raptorial or predaceous type. Belongs to the Dolichopodidze, and resembles Aphrosylus in the structure of the legs, but has dissimilar mouth-parts. It is a small Australian insect, which I captured at Geelong, Vic. Fig. B.-Fore leg of Notiphila cincrea Fln. 9. Raptorial type. It has the remarkable saw-like process on the femur, found also in many of the Hydrellinse. It is placed in the Ephydrids, is an inhabitant of damp places, and is rare in my experience. Fig. 6.-Middle leg of Caricea tigrina F. 8. Raptorial type. Placed in the Anthomyidse, but is fiercely predaceous. Common in damp meadows. Aug. 19th, 1908 2E 402 Transactions of the Society. are yet a matter of conjecture; indeed, the amount of care and patience required for the working out of these are sufficient to deter all but the most enthusiastic. I do not think that the work of the field naturalist, the accurate and minute noting of habit and life-history, can be overvalued, but I would point out another method, which, while it cannot supersede, can absolutely confirm as well as suggest further observation, and by its unaided use show a great number of structures, that on account of their minute- ness are visible by no other means. This method I have applied mainly to the insect in the imaginal stage,.which, owing to the quickness of movement in life, is the most difficult of observation, but it can be used with advantage in the study of the more simple larva. It has often been my experience to hear speakers depre- ciate the method of those who mount whole insects with pressure, the softer parts being dissolved and the object cleared in caustic potash. Their objections are good from many points of view, but the fact remains, that this method is the only one that will enable the student to use the higher powers of the Microscope ; and it is jiist this use of the high powers that is absolutely necessary for a complete study of a preparation, which when well mounted, ex- hibits all points of structure, and of difference other than colour, that the examination of a pinned specimen can show, and multi- tudes of detail that are beyond the powers of resolution of the simple lens. It is true that allowances have to be made for altered shapes and relations, but experience and study will give an idea of the changes undergone, and enable the student to reconstruct the original form of his subject in a mental image. I shall endeavour to show that it is possible to take a prepara- tion of an insect that may be quite unfamiliar, and sitting by a comfortable fireside, with a Microscope conveniently arranged, study it: (1) place it in its particular order, family and genus; (2) ascertain its sex ; (3) describe its habits, whether blood-sucking, predaceous, or otherwise ; (4) show how it obtains its food or attacks its prey ; (5) tell what that food is, sometimes naming the animal, plant, or insect, that serves as such; (6) know if it crawls on the earth, flies in the air, swims in or skates on the water, or is para- sitic ; (7) see how the insect smells, tastes, hears and feels ; (8) trace the differences that shade from species to species; (9) see the remains of the organs of the past, examining their minute remnants ; (10) see that there is nothing in Nature that is not logical and has not a “why and a wherefore”; (11) and be convinced that all these observations strengthen and fit in with that great fact of Evolution, which has so altered, for the man who thinks, the aspect of the earth as well as that of the heavens. But the field of inquiry is so large and the mass of detail so bewildering, that the student of ‘‘ life-history ” must use method in his investigations, and it appears to me that he will best obtain data bearing on his The Microscope and Biology. By W. Wesche’. 403 inquiry by a separate study of the parts. They may be divided thus :- ~.-GENERALSTRUCTURE. This includes, in addition to the insect as a whole, (a) the limbs ; (6) the finer bristles ; (c) the sense- organs. II.-THE ARMATUREOF THE MOUTH. III.-THE CONTENTS OF THE ABDOMEN: (a) food ; (b) structure. IV.-THE GENITALIA. I.-GENERAL STRUCTURE. This may be regarded from several points of view, as it is (A) Utilitarian ; (B) Sensorial ; (c) Raptorial ; (D) Secondary sexual. A. Utilitarian.-A study of the wings and their nervation affords information as to the character of the flight, but also is in a measure a guide that will tell something of the evolution of the species. The openings of the tracheE on the thorax and the abdomen show us how sounds are made, and how the insect oxy- genates the blood. The immense importance of keeping the antems clean is shown by the contrivances on the fore limbs, such as the brush on the metatarsi of the Muscidae, or the comb on the tibise of the Hymenoptera. The Microscope will show how it is possible for an insect to skate on the surface of smooth water, and para- sitism can be recognised by the flattened form of the body and the character of the legs, particularly the claws. B. Sensorial.-This section requires almost exclusively high- power work, and will in some cases necessitate the cutting of sections. All or most of the many modifications, such as “taste hajrs,” or “ olfactory pits,” and other structures so clearly brought before us in “ Senses of Animals,” * can be seen on preparations mounted with pressure : they must be looked for on the antennae and mouth-parts.? On the, legs will be found some sense-organs, particularly in Diptera, which are comparatively rare, and which I have described in a former paper : those on the cox= are more frequently met with than the organs on the tibiae.$ c. Raptorial.-Under this heading I include all modifications that are used in holding prey. The most usual characteristic is an enlargement of the femur to contain the much-developed muscles, and the legs and often the fore coxae have rows of strong sharp spines. But strong spines are equally characteristic, and the arrangement is apt to alter in different families. This type is usually easily recognisable, as it is found in both of the sexes, but there are a number of genera in the Syrphidze which, from the * Senses of Animals, 1889, Sir John Lubbock. t Sopra certi organi di senso nelle antenne dei Ditteri. Dr. Paul Mayer, Reale Accademia dei Lincei, 1878-79. t Some New Sense Organs in Diptera. Journ. Quekett Micr. Club, 1904. 232 404 Transactions of the Society. general appearance and detail of some of their limbs, as well as the armature of the mouth, might be thought to be raptorial, were it not that the convincing evidence atTorded by the contents of their stomachs exonerates them-(Ascia, Erystalis, Heliophilus, ikfallota, Xylota, and Syritta). In some of the genera of the Ephydridq there is a serrated fore femur, the chitin itself being drawn out into a number of sharp teeth, exactly like those of a saw ; this is unusual, most of these contrivances consisting of strong hairs in sockets. D. Xecondary sexual.-These structures are more strikingly developed, and more commonly found in the male sex; they mostly consist of an extraordinary variety of modification of the legs, usually of one particular pair, and often of the abdomen. Set= are altered in shape and grouped in rows ; they are, as a rule, blunter than those found on the raptorial limb, and occa- sionally take the form of bunches or pads of quite soft hair. Sometimes n seta is provided with a round head, not unlike that of the ordinary pin. In many cases the shapes of the tibiz are modified, and more often the tarsi are greatly enlarged, spatulated EXPLANATION OF PLATE VI. Fig. 7.-Hind leg of Leptogaster cylindrica Deg. 0. Raptorial type. Belongs to the Asilide, the most predaceous family in Diptera. Fig. &-Fore leg of Hilara clypcata Mg. 6. To illustrate the secondary sexual type. The extraordinarily enlarged metatarsus is used in holding the female, whose fore leg is quite simple.