420 PHYSIOLOGY. 



last segments of their body, in which, indeed, no distinct sucking-cups 

 are visible, but merely wart-shaped stumps of feet, at least upon the 

 last. This form, which we observe in the larvae of most of the Diptera, 

 is consequently the lowest of all. And, indeed, what is still more, not 

 merely in the organs of motion, but also in the mouth, do they resemble 

 each other, the former, like the latter, possessing short hard-pointed 

 puncturing instruments, with which they pierce their food and then im- 

 bibe it. The second grade of larvae, namely, those maggots which are 

 provided with a head, but are without feet, as, the larvae of the Hy~ 

 menoptera, and of many beetles, repeat another grade of the Annulata, 

 in which, as in Nais, there is a distinct head, but the feet are wanting. 

 The third grade of the Annulata, namely, those \vhich reside in tubes, 

 and are furnished with large bundles of gills, find, among insects, their 

 representatives in those larvae of the May and caddis-flies, which dwell 

 in cases and breathe through gills. The fourth grade of Anmdata, as 

 Nereis, Eumolpe, Aphrodite, &c., has, besides a distinct head, many 

 feet on the ventral side of the segments, and their analogies are, among 

 insects, the caterpillars of the Lepidoptera, and those larvae of the beetles 

 which are furnished with feet. 



In the pupa state, the insect advances into the class of the 

 Malacostraca. Just as the pupa state is a mere transition in the 

 life of the individual, so also is the class of Malacostraca a true 

 transition group in the development of the Arthrozoa, for the Arthrozoa 

 contained in it strive to detach themselves from the life in water to 

 elevate themselves to the life in air. Thence arise the innumerable 

 different forms, and, indeed, the greater difference between the indi- 

 vidual organs found in them more strongly than elsewhere ; with perhaps 

 the exception of the amphibia, which stand in the same relation to the 

 vertebrata : and the advance from the life in water to the life in air is 

 nowhere observed more distinctly than in the order of the Malacostraca. 

 The Crustacea are true water animals ; they all live in this element, 

 and quit it rarely and as an exception. The Myriapoda stand upon 

 the confines between the water and earth-dwellers: some incline to the 

 former and others to the latter. The Arachnodea, lastly, are true 

 earth-dwellers, particularly the scorpions, but some true spiders seek 

 the air as their medium, for they distend their web upon elevated 

 sunny places, and, floating in it, seem to endeavour to revel in the 

 purer air ; and, indeed, a few raise themselves upwards in the air, for 

 instance, A. oblectrix, which is raised by the wind upon its self- formed 



