2S 



GENERAL PRINCIPLES OF ZOOLOGY 



sliott'ii that they pass Ihroui^h a iiauplius-staLjc (Tig. 6a), characlcrislic 

 of most Crustacea, and that they tlien assume tlie shape of small Crustacea 

 (t\'^. 6, b), like Cyclops (lig. 7, .1), so \viclely distributed in fresh ^^■aters. 

 Very often the males make a halt in the cyclops-stage while the female 



Fig. 5. — Sifcdon pisci/onnis l,lar\"Li of A mhlv^^lonia tigritnuu) l^alLcr Dunit'ril and 



lUl)roii). 



develops farther and assumes a shapeless form, so that there arises a vcr)'- 

 remarkable sexual dimorphism (iig. 8). All these examples, which can 

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



Fig. 6.- 



Aiiilhci-rs jHrcanii:: . ,/, iiauiilius-, /., cyclops-stage; i, aduU female (after 

 Claus). 



forms pass through the stage of the lower, because they spring from an- 

 cestors which were more or less similar to the latter. Man in his em- 

 bryological de^-elopment passes through the lish stage, the frog the 

 perennibranchiate stage, the parasitic crustacean first the nauplius- 



