|3fljwlar 23tctf0narg of Ilirimatcll jtature. 345 



are in a few days hatched, and the young 

 larvx, which resemble minute white mag- 

 gots, subsist on the juices of their victim, 

 but without absolutely destroying it : in 

 fact, the animal they infest may continue 

 to exist for some time, thus alfording them 

 a continued supply of nutriment ; but when 

 the Ichneumons are ready to undergo their 

 last metamorphosis, they pierce the skin, 

 and each spinning itself up in a small oval 

 silken case, changes into chrysalis, the whole 

 number forming a group on the shrivelled 

 body of the caterpillar ; and, after a certain 

 period, they emerge in the state of complete 

 Ichneumons. One of the most familiar ex- 

 amples of this process is aiforded by the 

 caterpillar of the common white or cabbage 

 butterfly, which in autumn may be fre- 

 quently observed to creep up some wall or 

 other convenient surface, in order to under- 

 go its own change into chrysalis ; but in 

 the space of a day or two a numerous tribe 

 of small maggots will be seen to emerge 

 from it, and immediately proceed to envelope 

 themselves in distinct yellow silken cases ; 

 the whole forming a group around the cater- 

 pillar. The perfect Ichneumons feed solely 

 upon the juices of flowers, and fly about with 

 considerable agility in search of their food, 

 or of proper situations for the deposition of 

 their eggs. 



These carnivorous insects are of various 

 sizes ; some are so small, that the Aphis, or 

 plant-louse, serves as a cradle for their young ; 

 others again, from their size and strength, 

 are formidable even to the spider, destroying 

 them with their powerful stings : some place 

 their eggs within the aurelia of a nascent 

 insect ; others deposit them within the nest, 

 which the wasp has curiously contrived for 

 her young ; and, as both are produced at the 

 sama time, the offspring of the Ichneumon 

 not only devour the young wasps, but the 

 whole supply of larvae which the parent had 

 carefully provided for their support. The 

 best known, and perhaps the most formida- 

 ble of this genus, is the common Ichneumon 

 with four wings like the bee ; a long slender 

 black body ; and a three-forked tail, con- 

 sisting of bristles, of which the two exterior 

 are black, and the central one is red. But 

 when we read that " probably more than 

 3000 species exist in Europe alone, and the 

 number peculiar to other parts of the globe 

 may fairly be reckoned as at least equal," 

 it would seem to be of little use to attempt 

 to give more than this general description : 

 we shall therefore conclude by remarking, 

 that however terrible to other insect tribes 

 the Ichneumon-flies may be, their destruction 

 of countless myriads, which would otherwise 

 be left to banquet on the fruits of the earth, 

 must be of the most essential service to man- 

 kind. 



ICHTHYIAETUS. A Bub-genus of the 

 Falcon family of birds, so named from their 

 living principally on fish. From the account 

 given in Mr. Gould's work, some members of 

 the genus would seem to partake of the habits 

 of the vulture family : among these is the 



ICHTIIYIAKTliS LEUCOGASTER, of WHITE- 

 BELLIED SEA EAGLE. This is a fearless 



and familiar bird, found throughout the 

 whole of South Australia. It is distin- 

 guished by its never plunging beneath the 

 surface of the water, but living on dead 

 cetacea. fish, &c., left on the shore by the 

 tide. In Bass's Straits it subsists principally 

 on Petrels and Penguins, which are easily 

 captured. On the main land it builds a 

 large flat nest on a fork of the loftiest trees, 

 on islands, on the flat surface of a large 

 stone, and sometimes on the twigs and 

 branches of barilla, a low shrub. One nest 

 was observed on a tree 200 feet high and 

 41 feet round, where it probably had its nest 

 for several years. 



ICHTHYOSAURUS, or FISH-LIZARD. 

 A genus of extinct marine animals which 

 combined the characters of saurian reptiles 

 and fishes, with some peculiar to cetaceous 

 mammalia. This extraordinary creature, 

 whose fossil remains discover Its anatomical 

 conformation, has been the subject of much 

 learned investigation ; and the anatomy and 

 animal economy of it are in a manner esta- 

 blished. Some of the largest exceeded thirty 

 feet in length ; and, from their structure, it 

 is easy to conceive that they must have been 

 very formidable enemies to the other in- 

 habitants of the deep. The spinal column 

 was formed like that of a fish, the vertebra 



ICHTHYOSAURUS COMMDNIB. 



being concave on both surfaces, and the 

 arches which enclosed the spinal chord al- 

 ways remained distinct from the bodies as 

 in reptiles ; hence the body must have had 

 great flexibility ; but the progression of these 

 animals through the water was chiefly by 

 means of the anterior and posterior extre- 

 mities (of which there were four), formed 

 very much upon the plan of the feet or pad- 

 dles of the whale. The general form of the 

 head was not unlike that of the porpoise ; 

 and it had an elongated and pointed muzzle, 

 the mouth being armed with numerous cro- 

 codile-like teeth ; and its body terminated 

 in a long and powerful tail. From the ab- 

 sence of any remains of scales or plates, it 

 may be concluded that the skin was naked, 

 like that of the whales and their allies ; and 

 that it was an air-breathing animal, coming 

 to the surface of the water occasionally, no 

 doubt exists. From the remains of crushed 

 and partially-digested fish bones and scales 

 which are found with their bones, it appears 

 that the Ichthvosauri principally preyed 

 upon fishes. Dr. Buckland states that the fos- 

 sil remains of 'these animals abound along the 

 whole extent of the lias formation, from the 

 coasts of Dorset, through Somerset and Lei- 



