128 PHYSIOLOGY OF THE INVERTEBRATA 



of many of the Incertebrata is devoid of corpuscles ; and the 

 young of many of these animals (which in the adult form 

 have corpusculated blood) have blood without corpuscles. 

 This is another fact which proves that " development is a 

 progress from the general to the special, from the lower to 

 the higher form, and that the earlier stages of the history of 

 higher animals are similar to the adult forms of lower 

 ones." 



Although many forms of the Invertebrata have blood 

 devoid, or nearly devoid, of corpuscles, other forms have 

 corpusculated blood. 



The Actinozoa and Echinodermata. 



^'ch^l 



The " cnylaqueous *' fluid in the Actinozoa and EcJiinodcrmata 

 is analogous to the blood of higher forms. In both these 

 classes the blood is corpusculated : some of these corpuscles 

 are distinct cells with wall and nucleus, but the majority of 

 the corpuscles in the blood of the Actinozoa and Ecliinoder- 

 matct are of a very rudimentary nature. " They are probably 

 small masses of matter with no definite limiting membrane 

 on their exterior, akin, perhaps, to the albuminous molecules 

 in our chyle." 



The Myriapoda. 



In this class the blood is contained in some part of its course 

 in blood-vessels. It contains three distinct corpuscles, which 

 are devoid of cell-walls. " The simplest kind are pellucid 

 central nuclei invested by a few granules. Next rank the 

 oat-shaped corpuscles, where the nucleus is still very evident. 

 The third and most perfect form presents a central nucleus, 

 surrounded and almost obscured by a large number of 

 granules. As yet no definite cell-wall is to be seen on the 

 exterior of the granules." 



