HISTORY OF ZOO LOOT. 



37 



shown that they pass through a nauplius-stage (fig. 6), charac- 

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

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



ctu 



FIG. 7. Cyclops coronatus (A) and also the nauplius in lateral (B) and in ventral view 

 (G). I, head; II- F, the five thoracic, and behind these the five abdominal seg- 

 ments ; F, furca ; 1, the first, 2, the second, antennae ; 3, mandibles ; 4, maxillae: 

 5, maxillipeds ; 6-9, the first four pairs of biramous feet, while the rudimentary 

 fifth pair are hidden ; cm, eye ; o, upper lip ; e, egg-sacs ; (7, gut ; m, muscle. 



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

 cy clops-stage while the female develops farther and assumes a 

 shapeless form, so that there arises a very remarkable sexual 

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

 by hundreds, can be explained in the same way. The higher forms 



