OF DIGESTION. 35J 



fore always remain apterous, whereas those of insects and 

 mollusca are parasitic only as larvae, and acquire wings after 

 quitting this mode of life. The former belong in general to 

 orders with an imperfect metamorphosis, and the latter to 

 those with a perfect transformation. The remarkable genus 

 Braula, discovered by Nitzsch, which most probably belongs 

 to the family of Diptera pupipara, and which is parasitic 

 upon the honey bee, makes an exception; it is parasitic 

 during its whole life upon cold-blooded creatures, but is 

 also apterous, whereas the allied genera Hippobosca and 

 Ornithomya, although dwelling upon warm-blooded ones, yet 

 have wings. There are many other insects besides the para- 

 sites which feed upon animal juices, for example, the Asilica, 

 which seize other insects, and by means of their long proboscis 

 suck out all their juices ; the Tabanica, which sting men and 

 animals, and derive sustenance from their blood, besides many 

 genera and species of the numerous family of gnats, for 

 example, Culex, Ceratopogon, as well as the allied genus 

 Simulia; lastly, the larvae of the Dytici, which suck out 

 insects, like spiders, by means of their large hollow mandibles, 

 which are opened at their apex : the only analogy among 

 perfect insects to this structure of the mandibles is to be 

 found in the hollow proboscis of the Lepidoptera, whereas 

 in the spiders it is the usual and most common form. 



6. Corrupt animal juices. 



These are the same as those mentioned under I. 1. b., viz., 

 the impure juices of carrion and dung; they are voraciously 

 sucked up by many flies, for instance, Musca Caesar, Scato- 

 phaga pulris, Scybalaria, &c., and are even lapped up by the 

 Coleopiera, whose oral organs are less adapted to manduca- 

 tion, as was fully shown in the preceding paragraph. 

 2. From the vegetable kingdom. 



a. Fresh vegetable juices are sucked up by many insects, viz., 

 the Cicada, bugs, and Aphidce, as well as the species of 

 Chermes and Coccus. The majority pierce young one-year 

 shoots, and thereby so exhaust them that they die, particu- 

 larly when, as in the Aphides, they are found in hosts upon 

 one shoot. Almost each species selects a distinct plant, and 

 it is frequently the case that they are to be found upon that 



