HISTORY OF ZOOLOGY. 



37 



shown that tliey pass through a naupliiis-stage (fig. Ga), charac- 

 teristic of most Crustacea, and that they then assume the shape of 

 small Crustacea (fig. 6, i), like Cyclops (fig. 7, A), so widely dis- 



IJ 



Fig. 7.— Ci/f!o)« enroiiatuf: (A) and also the nauplius in lateral (B) and in ventral view 

 (O- I, head; II~V, the five thoracic, and beliind these the five aiidominal seg- 

 ments ; I'\ furca ; 1, the first, 2, the second, antenna ; 3, mandibles ; 4, maxilhe: 

 !), maxillipeds ; (j-!j, the flr.st four pairs of biramous feet, while the rudimentary 

 fifth pair are hidden ; au, eye ; o, upper lip ; c, egg-sacs ; i(, gut ; iii, muscle. 



trihuted in fresh waters. Very often the males make a halt in the 

 cyclops-stage while the female develops farther and assumes a 

 shapeless form, so that there arises a very reniarkal.ile sexual 

 dimorphism (fig. 8). All these examples, which can be multiplied 

 by hundreds, can be exjilained in the same way. The higlier f(n'ms 



