CRUSTACEA. 



129 



fore any one had the slightest idea that the Crustacea passed through 

 a metamorphosis, these six-footed larval forms were regarded as adults, 

 and were described as belonging to the genus Nauplius ; and to-day 

 this same term is retained to designate a peculiar larval stage, occur- 

 ring not only in the development of the fairy-shrimp, but in many other 

 Crustacea. 



Forms closely allied to the fairy-shrimps, both in structure and general 

 appearance, occur in all parts of the world. It is frequently stated that 

 there is no life in the great Salt Lake of Utah, but this is not the fact ; for 

 one of these fairy-shrimps occurs there in immense numbers, along with 

 larvae of one of the flies to be described farther on. A similar form is 

 found in the salt-vats at Syracuse, while another locality deserves a 

 moment's attention. All along the New England coast, where railroads 

 cross arms of the sea, tubs of water are kept on the bridges to be used in 

 case of fire. As the water evaporates, more is added from the sea below, 

 so that soon the tubs contain brine. In these tubs one frequently finds 

 these same forms. AVhence they came is a question. Nothing like them 

 occurs in the sea, and where their eggs could have come from, no one 

 knows. 



Besides the fairy-shrimps two other 

 types of leaf-footed Crustacea occur. In 

 the one the body is enclosed in a bivalve 

 shell which so closely resembles that of 

 one of the molluscs, that did one not open 

 the valves and see the shrimp inside, he 

 would not have the slightest idea that it 

 was a relative of the crabs. In the other 

 type, the general appearance of which is 

 shown in our cut, the anterior part of the 

 body is covered with a shield, but on the 

 under side are the same type of feet as 

 in the fairy-shrimp. These forms occur 

 somewhat abundantly in Europe. In the 

 eastern United States there are none, but 

 in the pools west of the Mississippi they 

 sometimes occur in great abundance. It 

 is a peculiar fact that among these forms 

 males are but very rarely seen ; indeed, of 



the European species Apus cancriformis no males were known until 1858. 

 The late Professor Carl von Siebold of Munich, who studied these forms, 

 bunted a long; time for the males. " On one occasion he had the whole 



Fig. 117.— Lepidurus (Apus lack- the paddle- 

 like plate between the caudal appendage). 



