PLANARIA ARETHUSA. 85 



All this, however, will prove of little as- 

 sistance in explaining how monstrosities by 

 excess are artificially produced, while we 

 should rather conclude that they ought to 

 terminate in defect. 



Planaria Arethusa, Fig. 11, 12, 13, 14. 

 Naturalists have affirmed that some plana- 

 ria3 are entirely destitute of any semblance 

 to eyes ; an opinion which, in one well- 

 known species, we have proved to be falla- 

 cious, and possibly it might be found equally 

 so respecting all others, or almost all, were 

 they rigorously examined. Reflecting on 

 the transcendant privileges which a sense 

 of inestimable value confers, we shall cease 

 to wonder at the solicitude of physiologists 

 to ascertain whether it has been dispensed 

 with in the structure of the smaller ani- 

 mals. 



But there are various planariae whose vi- 

 sual organs are better characterised, both 

 in site and appearance, than by clusters of 

 specks on the upper surface, as in the Flex- 



