XI 



PHYLUM ARTHROPODA 



635 



larva or " maggot " is completely worm-like, without any appen- 

 dages, and without any distinct head. In other cases (Lepidoptera, 

 &c.) there is a distinct head ; the three thoracic segments have 

 three pairs of jointed legs, and the abdominal segments short 

 unjointed pro-legs (Fig. 523). In most instances the larvae differ 

 widely from the adults in their food and mode of life ; very generally 

 the jaws are adapted for biting, even when the mouth of the adult is 

 suctorial. After a longer or shorter period passed in this larval 

 condition, in which it is usually active and very voracious, the 

 young Insect passes into a quiescent or pupa stage, during which 

 it remains passive, en- 

 closed in a tough integu- 

 ment, while a more or less 

 complete reconstruction of 

 the organs goes on, result- 

 ing in the development of 

 all the parts of the perfect 

 Insect. The development 

 of the new parts takes 

 place from certain patches 

 of cells, the imagined discs, 

 present in the larva. 



In the Diptera the larva 

 or maggot is sometimes 

 completely devoid of jaws. 

 In some Diptera, how- 

 ever, the jaws are well 

 developed, and there is a 

 distinct head. After fre- 

 q u e n t moultings the 

 maggot passes either into 



a quiescent Or pupa Stage FlQ . 540. J. an_d B, later stages of thT embryo of 



enclosed in a hard skin, or 

 into the stage of an active 

 aquatic pupa, which swims 

 about actively in water 

 and may possess tracheal 

 gills. 



In the Lepidoptera the larvae (" caterpillars ") are worm-like, 

 but with well-developed jaws, three pairs of jointed thoracic legs, 

 and a number of unjointed stumpy abdominal legs (pro-legs). 

 Lepidopterous larvae are often brilliantly coloured, are very active, 

 and feed with voracity, chiefly on leaves and other succulent parts 

 of plants. Eventually they spin a cocoon of a silky substance, 

 enclosed within which, and covered with a tough skin, they pass 

 through a quiescent or pupa condition the condition of the 

 chrysalis (Fig. 523). From the interior of this the imago subse- 



Hydyophilus with the rudiments of the ex- 

 tremities ; in B the abdominal appendages are 

 visible, a. anus ; an. antenna ; g, rudiment of the 

 ventral nerve-chain ; m. mouth ; md. mandible ; 

 mxi, first maxilla ; mxz, second maxilla ; PI, P2, 

 P4, thoracic legs ; p, p 5 , p 7 , p$, rudiments of the 

 appendages of the first, second, fourth, and sixth 

 abdominal appendages ; st. stigmata ; vk, prosto- 

 mium. (From Lang, after Heider.) 



