ii6 COMPARATIVE PHYSIOLOGY 



high on account of the structure of the circulatory system. 

 The blood-spaces are continuous ; the cavities in which the 

 blood flows are derived from the primitive blastocoel of the 

 embryo, where the latter is not filled with strands of con- 

 nective tissue and gelatinous material. Only in the larger 

 ascidians do connective tissue cells lining these lacunae limit 

 well-defined tubes, such as those formed by evagination into 

 the substance of the test. 



In conclusion, some mention is due to the peculiar character 

 of the blood in some Tunicates. In the colourless plasma, 

 there are in addition to amoeboid and spherical unpigmented 

 corpuscles, others packed with large granules of green colour 

 and markedly acid reaction. It is curious to note that the 

 green pigment is a compound of Vanadium and a protein. 

 The low oxygen-capacity of the blood makes it practically 

 certain that this is not a respiratory pigment. Clotting as 

 in crustacean blood is brought about by agglutination. 



References 



Alsberg (19 1 4). The Proteins of the Blood of Limulus. J. Biol. Chem. 



19. 

 Brucke and Satacke (1912). Der Arterielle Blutdruck des Hummers. 



Zeitschr. Allg. Physiol. 7. 

 Dakin (1908). The Osmotic Concentration of the Blood of Fishes, etc. 



Biochem. J. 3. 

 Carlson (1904-5). Nervous Origin of the Heart Beat in Limulus. Am. 



Journ. Physiol. 12. 

 (1906). Chemical Conditions of Heart Action in Limulus. Ibid. 16. 



(1905). The Comparative Physiology of the Invertebrate Heart. 



Ibid. 13-14. 



(1922). A Note on the Action of Drugs on the Invertebrate Heart. 



Journ. Gen. Physiol. 4. 



Carlson and Meek (1908). On the Mechanism of the Embryonic Heart 



Rhythm. Am. Journ. Physiol. 21. 

 Fredericq (19 1 3). Recherches experimentales sur la physiologic cardiaque 



d'Octopus. Arch. Int. Physiol. 14. 

 Fry (1909). The Influence of the Visceral Nerves on the Heart of Cepha- 



lopods. Journ. Physiol. 39. 

 FucHS (1908). Beitrage zur Physiologic des Kreislaufes bei den Cepha- 



lopoden Pflugers Archiv. 60. 

 Hart (1924). L'action des ions sur les mouvements rhythmiques du sac 



muscule cutane du lombric. Arch. Neerland. Physiol. 9. 

 Hecht (191 8). The Physiology of Ascidia atra. Am. Journ. Physiol. 45. 



