608 



SATYR1UM SAWFLY. 



have made its escape from an entire cocoon. Mei- 

 necken * has also suggested that the pressure of these 

 converging threads upon the abdomen of the moth as 

 it emerges from the cocoon has the effect of forcing 

 the fluids to enter the nervures of the wings, and give 

 them the proper expansion, having noticed that 

 moths produced from chrysalides taken out of their 

 cocoons were crippled in their wings. 



SATYRIUM (Linnaeus). A genus of tuberous- 

 rooted herbs, natives of the south of Africa. The 

 genus belongs to OrchidacetE,, and, like the rest of 

 the order, bears curious, though not very showy 

 flowers. They grow in sandy peat earth, and require 

 the protection of a frame in winter. 



SAWFLY (SERRIFERA, Latreille). The Eng- 

 lish name for a very extensive group of hymenopte- 

 rous insects, composing the Linnaean genus Ten- 

 thredo, and modern family Tenthredinidce, distin- 

 guished by their large wings with many cells, the 

 abdomen united to the body by its whole breadth, 

 and terminated on the underside by a pair of organs 

 (ovipositors), which are employed in the act of 

 depositing the eggs something in the same manner as 

 the common hand-saw of mechanics, whence the 

 popular name of the family. The construction of 

 this pair of instruments is, however, so much superior 

 to that of the hand-saw, and exhibits so admirable 

 an instance of contrivance in its design for a deter- 

 minate purpose, that a minute account of its structure 

 will not be uninteresting. Of course, the particulars 

 cannot be observed without the assistance of a 

 microscope, or high-powered lens ; and when these 

 are employed, it will be found that almost every 

 species varies in some one or other particular. The 

 eggs of these insects are deposited in the bark of 

 trees, the twigs of various plants, or within the 

 epidermis of the leaves, in which a slit is first 

 formed, into which the eggs are successively intro- 

 duced. The eggs have indeed somewhat of an 

 analogy to vegetable nature, as, for a certain period, 

 they increase in size, in consequence, as is supposed, 

 of imbibing the fluids of the plants into which they 

 have been introduced by the saws. The dorsal seg- 

 ments of the abdomen are deflexed at the sides in 

 these insects, the terminal segment being produced 

 at the base beneath, towards the base of the abdomen, 

 forming a groove on the underside within which the 

 saws play, being, moreover, protected by two distinct 

 scaly plates. When the insect, therefore, is disposed 

 to make use of its saws, it widens the groove, and 

 extends what at first sight appears to be a single 

 membranous piece, but which is very soon perceived 

 to consist of two plates, each formed of two distinct 

 portions, constantly applied against each other when 

 at rest ; the lower half of each of these instruments, 

 that is, from base to tip, is the saw, and the upper 

 half of each constitutes the supports of the saws, 

 being formed with a groove somewhat like the 

 structure of a clasp knife ; iu each of these grooves, 

 therefore, one of the saws plays backwards and 

 forwards, the muscles at its base acting as the moving 

 power, and when these four pieces are brought into 

 contact, a central space is produced which serves 

 for the passage of the egg. The back, or support of 

 each saw, indeed, at first sight appears very similar in 

 its construction to the saw itself, being of equal length 



* Quoted by Kirby and Spence, from whom this account is 

 abridged. 



and breadth, with similar transverse, or rather slightly 

 oblique ridges ; but a more minute examination 

 shows them to be unfitted for action as sawing in- 

 struments. These ridges or oblique channels corre- 

 spond in number with the number of teeth in the 

 saw. It will be easily conceived that, from the sup- 

 port given to the supporting piece by the corneous 

 plate of the abdominal segment, it is well fitted for 

 enabling the saw to work backwards and forwards. 

 In the carpenter's saw there is somewhat of the 

 advantage of a double edge (which we here find pro- 

 duced by the presence of two saws), because the 

 teeth of the carpenter's tool are alternately directed 

 to the right and to the left ; and the groove between 

 the two lines made by the teeth, which is called the 

 course of the saw, is represented in the sawing of the 

 sawfly by the action of the two saws having straight 

 teeth. It will therefore be probably asked, where is 

 the necessity for two saws, when even the ingenuity 

 of man has effected a similar purpose with only one 

 saw ? and if the action of the insect had no other 

 object than that of sawing the plant, there might be 

 perhaps ground for the enquiry. But the insect has 

 another and far more important object to perform, 

 namely, the depositing of its eggs in the groove 

 made by the saws, which could not be done by a 

 single saw. At first sight the saw appears to be 

 composed of simple teeth, but the application of high- 

 powered lenses proves that one of the edges of each 

 tooth is itself furnished with very minute teeth, thus 

 combining the property of a rasp or file, in their 

 lateral action, with that of a saw in their vertical 

 movement. Moreover, the sawfly has the power of 

 working the saws alternately, a peculiarity necessary, 

 because, each works in the same channel, and not, 

 like the compound saws of artificers, in distinct lines. 

 More highly magnified powers, also, show that even 

 the membranous sides of the saws are furnished with 

 an infinite number of minute points, which, in all 

 probability, serve to irritate still more forcibly the 

 edges of the wounded part of the plant, causing it to 

 produce a greater supply of extravasated fluids, 

 which is serviceable for the development of the egg. 



A, extremity of the abdomen of the Sawfly, showing the two 

 saws c and their supports d extended ; a, the terminal joint of the 

 abdomen ; and b, the two internal horny sheaths. B, a small 

 portion of one of the saws very highly magnified. 



After the groove is rendered sufficiently deep, the 

 saws are made to conduct an egg into the place pre- 

 pared for its reception, immediately after which a 

 drop of frothy fluid is introduced into the hole over 

 the egg, of which the probable use is to close the 

 wound. Each groove contains but a single egg, and 

 there arc accordingly sometimes as many as a couple 

 of dozen of grooves to be made ; these are placed 

 in a line on the same branch, six of them occupying 



