ON THE HEART OF APPENDICULARIA FURCATA. 277 



beyond a certain point. After this point the typical organi- 

 sation itself is no longer maintained. The Rotifera are 

 reduced to the smallest possible size compatible with their 

 high organisation. The smallest exhibit loss of organs (e. g. 

 the ciliated canals), and appear to be at the extreme point in 

 reduction of the number of plastids, whilst Appendicularia 

 furcata is in a similar condition among Notochordate 

 Pharyngobranchiata. 



