TIIK CLASS 01 



gnishable from each other. Here we see the embryo divided 

 into a head-thorax and a tail. 



It is the saiiu- with Insects. Within the egg at the dawn of 

 life they are flattened oblong bodies curved upon the yelk 

 imi-s. Before hatching they become more cylindrical, the 

 limbs bud out on the sides of the rings, the head is dearly 

 denmrked. and the young caterpillar soon steps forth from the 

 ogg-shell ready armed and equipped for its riotous life. 



As will be seen in Fig. 8, the legs. jaws, and antenna. 1 are 

 first started as buds from the side of the rings, being simply 



elongations of the body-wall, 

 which bud out, become larger, 

 and finally jointed, until the 

 \x buds arising from the thorax or 

 abdomen become legs, those 

 from the base of the head be- 

 come jaws, while the antenna- 

 and palpi sprout out from tin- 

 front rings of the head. Thus 

 while the bodies of all articulates 

 Fig. 8. are built up from a common em- 



bryonic form, their appendages, which are so diverse, when we 

 compare a Lobster's claw with an Insect's antenna, or a Spider's 

 spinneret with the hinder limbs of a Centipede, are yet but 

 modifications of a common form, adapted for the different uses 

 to which they are put by these animals. 



Fie, >. A Caddis, or Case-fly ( Mytttuides) in the egg, with part of the yolk 

 <.r) not yet in:-l:>sed within the body-walls, a, antenna;; between n and h the mandi- 

 ble- : t>, maxilla; c, labium; '/, the separate eyc--pots (ocelli), which afterwards in- 

 crease greatly in number and unite to form the compound eye. The neck" or 

 junction of tac head with the thorax i- seen at the front part of the \ oik-mas- : . 

 .the three pairs of legs, which are folded once on themselves ;/. tin- pair of anal legs 

 attached to the tenth ring of the abdomen, as >een in caterpillars, which form long 

 antenna-like filaments in the Cockroach and May-fly, etc. The rings of the body arc 

 'but partially formed: they are cylindrical, giving the body a worm-like form. 

 Here, as in the other two figures, though not so distinctly seen, the antenna', jaws, 

 and last pair Of abdominal legs are modifications of hnl a -ingle form, and grow 

 out from the >ide of the body. The head-appendages are directed forwards, as 

 they are to be adapted for sen.-ory and feeding purposes ; the legs are directed 

 tio\v nward-. .-ince they are to support the in>ect while walking. It appea/> thai ll-e 

 n\<> ends of the body arc perfected before I he middle, and the under side before the 

 upper, as we see the yolk-mas., i> not yet inclosed and the ring* noi yet formed 

 above. Thus all articulates ditl'er from all vertebrates in having the yolk-mass 

 -ituale.lon the back, instead of on the belly, as in the chick, dog, or human em- 

 l>r\ o. From Zaddnch. 



