FEBRUARY 1, 1900.] 



KNOWLEDGE. 



33 



That ia the Natural Square the odd numbers all lie 

 in a diagonal cross, the even in a lateral cross. 



f/g 4. 



That in the !Magic Square the even numbers all He in 

 a diagonal cross, the odd in a lateral cross. 



In this respect therefore there is complete polarity 

 of direction between the two squares. 

 {To he continued.) 



THE FLY, "SYRITTA PIPIENS." 



By Walter Wesche. 



A CAREFUL study of the anatomy of insects, aided by 

 the higher powers of the microscope, though a pursuit 

 of great interest, taxes the observer's ingenuity to 

 account for the changed aspect of organs when ren- 

 dered transparent, flattened, and mounted under 

 pressure. The appearances presented are often likely 

 to lead to erroneous conclusions, unless one is ac- 

 quainted with the position and shape of the object in 

 its natural condition. A knowledge of the life-history 

 and habits of an insect is also essential if a correct idea 

 as to the uses and purposes of the several parts are to 

 be arrived at. For instance, thi-ie is a beautiful con- 

 trivance on the tibia of the forelegs of most of the 

 Hymenoptera, and some of the Coleoptera, for cleaning 

 the antennae, which, had not Mr. Frank Cheshire ob- 

 served its iise, would probably be still regarded as an 

 auditory organ. The great elaboration and speciali- 

 zation of different mechanisms for various purposes 

 displayed in the anatomy of insects are only equalled 

 by the economy of means ; every part is, or has been, 

 in some way, of use to its possessor, though what that 

 use is is often a difficult matter to divine. 



Syritta pipiens, with its complicated lancets (fig. 3) ; 

 the process of knife-like setse on the tibia of the fore 

 leg (fig. 6), which is usually found in predaceous flies 



Fio. 1. — Siiritla pipiens. Female. Femur 

 of hind leg flattened. 



and beetles, and used in holding prey ; the many 

 chitinous setse on the tarsi of the middle leg, disposed 

 in fairly regular patterns (fig. 5) ; and the remarkable 

 hind leg (fig. 4), which at first view seems adapted to 

 the curbing of the struggling wing of a powerful 

 opponent, might incline to the opinion that the fly was 

 raptorial, and used these parts in pursuit and capture 

 of its prey. The insect is very well known and common 



from April to October. It belongs to the family 

 Syrphidiv, or ' Hover flics," and feeds on the pollen of 

 flowers, of which its abdomen may often be found full. 



Via. 2. — S. pipinis. Male. 



It is figured and described under the name of Musca 

 pipiens in the work of the old French entomologist, 

 Dc Geer, and so exhaustively that most later writers 

 quote his observations (Westwood and othcr.s). It was 

 named from iU habit of uttering an exceedingly acute 

 cry when held, the sound being produced through the 

 two large pear-shaped spiracles on the thorax. De Geer 

 found the larvre in the dung of horses and cows; it is 

 thicker in front than behind, and has a small point on 

 the head. 



The male (fig. 2) is a little smaller than the female, 





Fig. 3. — Mouth organs uf .S'. pipiens, proliosfis, lancets, and 

 maxillary palpi ; smaller circle lias tip of lancet more magnified 

 and shoiving liairs. x 46 diameters. 



as is usually the case in insects, and the mouth organs 

 and legs do not differ, with the exception that the male 

 carries a series of very short chitinous spines on the 

 coxse of the hind leg — " a secondary sexual " character- 

 istic, enabling him to hold the female in a firm grip 

 (fig. 4). The same process is to bo found on the males 

 of Erystalis (bee or drone fly). The coxa; of the female 

 are quite plain, and both sexes have a pretty and 

 delicate fringe of hair on the abdomen to protect the 

 femur of the bind leg from the effects of chafing. The 

 male, in its markings, also differs from the female, 

 these ex;temal characteristics being larger and lighter 

 on the dorsal region of the abdomen, and there is a 

 smaller space between the eyes (facies). 



