THE CLA.SS OF INSECTS. 



j^iiishable from each other. Here we see the embryo divided 

 iato a head-thorax and a tail. 



It is the same with Insects. Within the egg at the dawn of 

 life they are flattened oblong bodies curved upon the yelk- 

 mass. Before hatching they become more cylindrical, the 

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

 demarked, and the young caterpillar soon steps forth from the 

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



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

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



elongations of the body-wall, 

 which bud out, become larger, 

 and Anally jointed, until the 

 buds arising from the thorax or 

 abdomen become legs, those 

 from the base of the head be- 

 come jaws, while the antennse 

 and palpi sprout out from the 

 front rings of the head. Thus 

 while the bodies of all articulates 

 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 tliey are put by these animals. 



Fig. 8. A Ciiddis, or C;ise-lly (.^^y■it'lc^(les) iu the ejjg, with pari of the yolk 

 (.r) not yet inc-loscd within the hixly-walls. ti, anteniiEe ; between a and h the mandi- 

 bles; b, maxilla; c, labium; il, the separate eye-spots (ocelli), which afterwards in- 

 '•rease trrcatly in number and unite to form the compound eye. The "neck" or 

 junction of the head with tlie thorax is seen at the front part of the yolk-mass; e, 

 the three pairs of legs, which are folded once on themselves ;/, the pair of anal \eg» 

 attached to the tenth ring of the abdomen, as seen in cateri)illars, which form long 

 antenna-like filaments in the Cockroach an<l May-fly, etc. The rings of the body are 

 i)ut ijartially formed; they are cylindrical, giving the body a worm-like form. 

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

 and last pair of abdominal legs are modifications of but a single form, and grow 

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

 tliey are to be adajited for sensory and feeding purposes ; the legs are directed 

 downwards, since they are to support the insect while walking. It appears that the 

 two ends of the body are perfected before the middle, and the under side before the 

 upper, as we see the yolk-mass is not yet imdosed and the rings not yet formed 

 .above. Thus all .-.rticulates differ from all vertebrates in having the yolk-niass 

 situated on the back, instead of on the belly, as in the chick, dog, or human em- 

 brvo. — From Zaddach. 



