MICROSCOPIC OBJECTS. 47 



Among" the most remarkable and it may be added 

 beautiful fossil shells of Infusoria are those recently dis- 

 covered in guano, especially that obtained from Ichaboe. 

 These remains, when separated from the animal and 

 earthy matters in which they are found, and mounted in 

 Canada balsam, exhibit all the delicate and symmetrical 

 structure of the recent species, with the addition of 

 brilliant tints. The latter pecuharity is not met with 

 in the shells of any other deposit. The genera of fossil 

 BaciUaria (most beautiful as regards colour) are the 

 Actinocyclus, Gallionella and Tripodiscus. 



Larvcs of Insects. — The young of insects when they 

 emerge from the egg are called larvce. They diifer 

 greatly in form and habits from the parent. In this the 

 caterpillar state they attain their full size, when they 

 become partially or wholly torpid ; they are now called 

 pupa, or chrysalides. During this period their internal 

 structure undergoes a marked change to prepare them 

 for the perfect state either of flies, butterflies, or beetles, 

 &c. In this latter condition alone are they able to pro- 

 pagate. Their metamorphoses are certainly the most in- 

 structive part of Entomology, although greatly neglected 

 until of late years. The remarkable change in the 

 habits of a creature from an aquatic mode of existence 

 to that of an aerial one, must be accompanied with as great 

 a change of structure adapting it to such different ele- 

 ments ; yet in the cabinet of the entomologist few if 

 any specimens wiU be found except those of the imago 

 state. The aquatic larvae were brought prominently 



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