114 EMBRYOLOGY OF THE PODOPHTHALMATA. 



on peduncles and the other characteristics of the fully-developed 

 animal. 



It is very remarkable that, unlike the Lepidoptera and Coleop- 

 tera, the Crustacea arrive at their final stage before they can be 

 said to have grown at all. If we take any of the insects, we 

 find that all the growing takes place during the larval state; 

 whereas, if we take as an example the common edible crab, 

 Cancer pagums^ we find that it reaches its final stage when very 

 minute. I have frequently taken it, developed, a quarter of an 

 inch only across the carapace ; and yet this species sometimes 

 attains a weight of 12 lbs., so that the amount of growth that 

 takes place during the Zooea form, as compared with the crab 

 form, is very small. 



There is no doubt that these curious Zooea forms constitute the 

 food of numerous fishes as well as other marine animals, and that 

 millions upon millions of them are thus destroyed ; were this not 

 so, the sea bottom could not afford standing room to the various 

 Crustacea that would be produced, for the number of eggs 

 deposited by one individual is something astounding. There 

 seems, however, to be a wide difference in the proportionate 

 numbers produced by different species; and it would appear 

 as if those species whose young are more especially liable to 

 this destruction were more prolific than those whose young are 

 not so liable, owing to their different mode of existence. 



For examination by the microscope these objects afford a wide 

 and comparatively new field ; and apart from the amount of infor- 

 mation which they furnish to the student of zoology, particularly on 

 that part of the subject which refers to the embryo stages, they are 

 also specially interesting on account of their great beauty when 

 shewn by means of dark ground illumination, as also on account 

 of the remarkable structure of the developing Zocea form of the 

 animals. 



In order to obtain the desired means of examination, it is 

 necessary, with such delicate organisms, to preserve them in such 

 a manner as shall retain their living appearance and form ; and at 

 the same time enable them to be mounted for microscopic 

 examination, not only temporarily, but for future reference. This 



