Abstract
1. In instituting a comparison between the blood-corpuscle, in its different phases of development, of the Vertebrata and that of the Invertebrata, it is obvious that the examples first taken for the purpose ought to be selected from the lowest class of the oviparous Vertebrata on the one hand, and from the highest class of the highest division of the Invertebrata on the other. 2. In accordance with this I proceed to compare together the blood-corpuscles of the Skate and Crab.