194 



FKESHWATER FAUNA 



this produces larger eggs than the marine forms, and also 

 enters upon life in a more advanced stage of development 

 than the mysis.* 



The freshwater crayfish bears its eggs with it, attached 

 to the swimmerets of the abdomen, like the lobster. The 

 young, however, unlike those of the lobster, are provided 



FIG. 66. The Development of the Marine Prawn 

 Peneus. 1. The first stage, or nauplius. 2. 

 The second stage, or zoea. 3. The zoea some- 

 what farther advanced. Magnified 20 diameters. 

 After Fritz Miiller. 



with sharply-hooked claws, by which they can hold on to 

 the parent after they have entered upon a free existence. 



As a result of this somewhat lengthy review it clearly 

 appears that the majority of freshwater animals are pro- 

 vided with one device or another, sometimes surprisingly 

 ingenious, for securing their place in a medium which is 



* Faxon, Bull. Mus. Comp. Zool Harvard, 179, p. 303 



