48 MICROSCOPIC OBJECTS. 



before the public by the authors of the 'Microscopic 

 Illustrations' and 'Cabinet.' Those works contain nume- 

 rous drawings of them ; and the circumstance of their 

 subsequently foraiing the staple material of the micro- 

 scopic exhibitions, proves the interest taken in them by 

 the public. In the Catalogue, a few only have been 

 given, from the difficulty the author has found in cor- 

 rectly naming the species or even the genera to which 

 they belong. The perfection and permanency in which 

 larvae may be preserved in Canada balsam, render it more 

 than probable that at no very distant period no entomo- 

 logical cabinet will be considered complete that does not 

 contain specimens of insects in the larva and pupa as well 

 as in the perfect state, to which may be added their eggs. 

 Then, and not till then, shall we be able philosophically 

 to understand the economy of these numerous and diver- 

 sified beings, and the important purposes they subserve in 

 the animal kingdom. 



The recent discoveries of the Danish naturaUst 

 Steenstrup, described in his work on the Alternations of 

 Generations, by which many of the lower classes of 

 invertebrate animals are developed, differ essentially 

 from the metamorphosis of insects. In insects neither the 

 larva nor the pupa has the organs necessary for increasing 

 or propagating its species. In fact, metamoi*phoses or 

 transformations only imply changes which occur in the 

 same individual. In those creatures which are developed 

 by " alternating generations " we see " the remarkable 

 and tin now inexpUcable natural phenomenon of an ani- 



