INSECTS AND OTHER ORGANISMS 409 



it develops within this second host into the characteristic 

 elongate, slender worm which after absorbing all the fat- 

 body and other internal organs of the beetle, bores its way 

 into the outer world to become mature in water or damp 

 soil. Gordius has been observed to attain a length of 

 over 120 mm. (about 5 inches) within the body of a Ptero- 

 stichus, whose cavity may be almost choked with the 

 parasites' closely packed coils. Long, slender threadworms 

 of the Mermis group, somewhat like Gordias in aspect but 

 belonging to the Nematoda, undergo their development 

 and attain almost to their full size in the bodies of various 

 beetles as well as those of grasshoppers and cockroaches. 

 Cockroaches and other insects often harbour several kinds 

 of Nematoda belonging to Oxyuris and other genera. A 

 species of Filaria, encysted as a larva in the fat-body of the 

 common Kitchen Cockroach {Blatta orientalis) becomes 

 mature in the digestive canal of the omnivorous rat. The 

 curious parasitic worms known as the Acanthocephala 

 which live when mature in the intestine of vertebrates have 

 several species whose larvae are parasites of insects. For 

 example, the large fleshy grubs of chafers may be infested 

 by larval Gigantorhynchns gigas ; if such a chafer-grub be 

 devoured by a rooting pig, the Gigantorhynchus will attain 

 its adult condition in the pig's digestive tract. 



The intestines of insects, like those of many other 

 animals, are often inhabited by large numbers of unicellular 

 organisms of the great group known as the Protozoa. Cock- 

 roaches harbour an assemblage of Rhizopoda, Gregarinida, 

 Infusoria, and Flagellata, many of which appear to be simply 

 parasites. Gregarines, Clepsidrina blattarum for example, 

 are found as minute, intracellular parasites in the epithelium 

 lining the cockroach's stomach ; they grow, extrude 

 from the host- cell, and becoming free in the gut- cavity 

 proceed to the pairing of individuals which precedes division 

 into gametes, conjugation, and the formation of resistant 

 spores. Elongate Flagellata belonging to Leptomonas 

 (Fig. 84, c) and allied genera often abound in the food- 

 canal of Hemiptera, Diptera, and other insects. A point 



