148 NATURAL HISTORY. 



and perhaps modified representatives of a group formed by the ancestors of the whole multitude 

 of insect types which we have here attempted to pass in review. 



The Thysanura have been considered by different entomologists to form either a distinct order or 

 a section of the Orthoptera, while some writers have even thought that they might rather be united 

 with the next class. Considering this diversity of opinion, and the real peculiarities of organisation 

 from which it springs, it seems best to treat these little creatures as actual members of the class of 

 insects, with which they most nearly agree in structure, but to give them prominence by ranking them 

 as a distinct order. At the same time, while an undoubted close relationship runs through all the 

 members of the order, there is sufficient difference in the groups of which it is composed to render 

 it difficult to formulate a set of characters which shall apply pretty equally to the whole. 



One primary character is to be found in the entire absence of wings, and of any metamorphosis ; 

 and a second, in the feebleness of the organs of the mouth, which are also generally concealed within 

 the cavity of the head. The eyes, when present, are almost invariably ocelli or simple eyes, either 

 placed singly or aggregated in groups on the sides of the head ; true compound eyes occur only in 

 one genus. The body is generally rather soft in texture, and has its surface clothed with peculiar 

 hairs and scales somewhat resembling those of the Lepidoptera, but of course much smaller*, some of them 

 being among the most delicate objects for the microscope. The lower surface of the abdomen is 

 usually furnished with appendages, as also the apex of that region in some species, and these, which 

 vary considerably in structure, serve in the majority as saltatorial organs. The members of this order 

 generally frequent obscure places, and some of them show a preference for moist localities, while 

 others delight in dryiiess and warmth. Their food consists of decaying vegetable matter. 



Sir John Lubbock divides them into two orders, the THYSANURA and the COLLEMBOLA. At the 

 same time, he shows that some members of the former group are very neai'ly related to those of the 

 second, and therefore we may take the two groups, which really agree precisely with the families 

 generally accepted by previous writers, and regard them as forming two great tribes of the same order. 



TRIBE I THYSANURA GENUINA, OR BRISTLE-TAILS. 



This group is distinguished by having long antennae composed of many joints, tarsi of from two 

 to four joints, and more or less exposed mandibles and maxillae. The maxillary palpi are often long, 

 and composed of five or seven joints, sometimes shorter, and only two-jointed ; the labium is more 

 or less cleft in front, and bears four-jointed palpi ; the prothorax is large ; and the under surface of 

 the abdominal segments, or of some of them, bears pairs of appendages (rods or tufts), besides, in 

 general, two or three long, jointed, caudal bristles. The body in these insects is almost always clothed 



with metallic scales, which closely cover the whole sur- 

 face, and give the creature a beautiful silvery appear- 

 ance ; but, unfortunately, these scales are rubbed off by 

 the lightest touch, and it is very difficult to capture 

 one of these insects without sadly spoiling its beauty. 

 In some respects, especially in the conformation of the 

 organs of the mouth, the more typical members of this 

 tribe, forming the family LEPISMID^E, approach most 

 nearly to the Orthoptera, and among the latter the 



LEPISMA SACCHARIXA. alliance would seem to be closest with the Blattidaa. 



Of this family a good many species are known, chiefly 



from different parts of Europe and the neighbouring countries, the largest of them being rather 

 more than half an inch long. Lepisma saccharine, a silvery creature like a little fish, is not un- 

 common in Britain, living in decaying wood, and also frequenting houses, where it commonly takes 

 up its abode in the sash-frames of the windows. It runs rapidly, but does not leap. In the genus 

 Machilis, two species of which inhabit Britain, the ventral segments are nearly all furnished with 

 paired appendages, and those of the ninth segment are converted into a springing fork homologous 

 with that characteristic of the next tribe. One British species (M. polypoda), which is brown with a 

 metallic lustre, is found in woods and dry places ; the other (M. maritima), a mottled brown species, 

 occurs under stones on rocky shores. These insects are about half an inch long. They have com- 



