316 



KNOWLEDGE ♦ 



[Nov. 23, 1883. 



PLEASANT HOURS WITH THE 

 MICROSCOPE. 



By Henry J. Slack, F.G.S., F.R.M.S. 



MOST of the older naturalists regarded species as 

 originating in distinct creative acts, and the natural 

 theologians following, or helping to mislead them, studied 

 every creature and every part of each creature upon the 

 supposition of special design and adaptation to the per- 

 formance of particular functions. According to such 

 theories the whole order of nature appeared as an exhibi- 

 tion of an infinite number of detached parts, and every 

 organ of any living thing as a contrivance like a tool made 

 by a skilful artisan. A stricter and wider examination of 

 plants and animals showed points of connection and lines 

 of transition. Descent does not invariably produce an 

 exact repetition of the parent forms, but sometimes modifi- 

 cations occur, which, if useful to the creature, and also 

 capable of hereditary transmission, give rise to varieties 

 and species, the latter being, in fact, only the former in 

 a lasting condition. Under the older conception, it was 

 impossible to explain the existence of obsolete parts no 

 longer useful, or of parts that did not work in the best 

 possible way. The newer and truer philosophy discovers 

 a unity of plan throughout Nature, and traces organs from 

 rudimentary beginnings to their completest development. 

 Eyes, for example, do not always see, as we understand 

 seeing. The simplest eye forms no image, but allows its 

 possessor to have some sensation of light ; and organs of 

 all kinds, which some creatures possess in an elaborate 

 condition of structure, may be found in simpler stages of 

 development in others. Another important fact brought 

 into view by recent investigations is that parts which are 

 morphologically the same may have widely different func- 

 tions to perform. It is well to bear these things in mind 

 when examining any of the interesting insects of the group 

 to which bees, wasps, ants, ic, belong, and a caution may 

 again be given to the effect that the more scientific view of 

 Nature does not militate against Natural Theology, but, 

 on the contrary, raises its character and strengthens its 

 evidence. 



The two orders Nemoptera and Hymenoptera are both 

 composed of four-winged in.sects, but while the former — 

 which are the best flyers — have equal wings, the latter have 

 the hind wings much smaller than the front ones. The 

 veins are also fewer, and do not produce the network 

 appearance characteristic of the Nemoptera. The Hymen- 

 optera have horny jaws, and tongues adapted to lapping, 

 or both lapping and sucking, as in bees, and their maxilke 

 close upon the tongues and form a sheath assisting their 

 action, as was explained in former papers. The females of 

 different kinds of Hymenoptera are furnished with stings, 

 saws, and ovipositors, very various in size and shape, 

 but in all cases essentially the same organs modified to 

 diflerent uses. The wasps and bees deposit their eggs in 

 cells which they build or dig out. Their stings assist in 

 directing the eggs to the right place, but their chief function 

 is warlike. They are weapons rather than ovipositors. The 

 gall - flys' instruments are borers as well as ovipositors. 

 They pierce little holes in trees, and, like the bees and 

 wasps, eject an irritating fluid which stimulates the plant 

 to develop the peculiar growth such as the nutgall, leaf 

 galls, and spangles of the oak, or the hairy bedeguar of the 

 rose, which serve at once as houses and larders for their 

 grubs. The saw-flies have their terminal organs modified 

 into saws, as their name suggests, with which they cut 

 slits in bark or leaf, and drop their eggs into them. The 



ichneumons work with slender tools, longer or shorter 

 according to their habits. They commonly insert their 

 eggs into the bodies of aterpUlars, and their grubs feed 

 upon their host so prudently that they do not kill it 

 until they are ready to emerge. A general description of 

 the ovipositors, stings, ic, is given as follows, by Mr. 

 Westwood. He remarks that " from the centre of the 

 underside of the abdomen, near its extremity, arise two 

 plates, each consisting of two joints, sometimes valvular, 

 and together forming a scabbard, sometimes more slender, 

 and resembling palpi, and sometimes very long ; between 

 these plates as they exist in the bee, under the form of two 

 flattened plates with a pair of terminal lobes, arise two 

 other pieces, which are very slender, serrated on the tip in 

 the bees, but much broader in the sawflies, and transversely 

 striated, forming the saws with which these insects are 

 provided." There are five or six parts in these tools, 

 though some are so often reduced in size as scarcely to be 

 noticeable. In bees and wasps the sheath is a strong pierc- 

 ing implement, and it holds in a groove two fine stings 

 which are worked by a mechanism that squeezes the poison- 

 bag at the time they penetrate the victim of the attack. 

 The serrated tips prevent their withdrawal out of any firm 

 substance, and consequently when the insect strikes an 

 enemy, it often inflicts a fatal injury upon itself. The 

 sting remains, and the creature's inside is terribly torn as 

 it drags itself away, and it soon perishes. If the sting 

 were a separate and independent construction, designed 

 entirely as a weapon, it might be compared with some of 

 the cheap guns sent Viy Birmingham to Africa, which cannot 

 be let ofi' without injuring the shooter ; but when its parts 

 are found to be modifications of a set of organs belonging 

 to large groups of insects, and subserving a variety of pur- 

 poses, we can admire them for what they will do, and think 

 less of their defects. 



The Queen Bee has a sting curved like aa Eastern 

 dagger, and uses it in a murderous duel with any rival 

 of her own sex, and the victor, if escaping whole from 

 the fight, has nothing more to do with war's alarms, and 

 if she does not turn her spears into pruning hooks, employs 

 them in the peaceful purpose of assisting in the deposition 

 of the many thousands of eggs she has to lay. 



The variations of structure and function which the 

 anatomist and physiologist trace in plants and animals 

 proceed according to laws very imperfectly understood. 

 Important modifications are concurrent, and mutually 

 adaptive. In the Hymenoptera the mouth organs and the 

 abdominal ones are suited to each other, and their internal 

 organisation corresponds. Bees and ants stand highest in 

 intelligence amongst insects. The order they belong to is 

 a very large one. In this country it is reckoned that we have 

 3,000 species. Amongst so many there is room for a great 

 variety of modifications, and it is very interesting to trace 

 them in their mouths, legs, abdominal instruments, and 

 nervous development. Insect phrenology is a very difficult 

 study, but small as the brain is in the ant and the bee, it 

 suffices for manifestations of intelligence as well as blind 

 instinct, which leads Sir J. Lubbock to say that the 

 chimpanzee and the gorilla must give way to them. All 

 these creatures have to take care of their posterity. The 

 bees store the honey that is to feed their young. " In the 

 case of wasps, the larva requires animal food, and the 

 mother therefore places a certain number of insects in the 

 cell, each species having its own special prey. Cerceris 

 hupreslida, as its name denotes, attacks beetles belonging 

 to the genus Bnpreslis. Now if the Cerceris were to kill 

 the beetle before placing it in its cell, it would decay, and 

 the young larva when hatched would find only a mass of 

 corruption. On the other hand, if the beetle were buried 



