602 



alimentary canal. The latter makes its appearance after the metamor- 

 phosis in the Actinotrocha from Beaufort Harbor, and I am quite 

 sure it represents the branches of the efferent vessel which pass up 

 around the oesophagus and become continuous with the recipient 

 vessel of the adult (Fig. 3 ef.h). It must be mentioned, however, that 

 Masterman says these branches open into the dorsal blood vessel 

 (afferent vessel of adult) which is not the case in the form on which I 

 have worked. 



The Actinotrocha which has just completed its metamorphosis 

 has only one ring-vessel (larval collar- cavity) but the young Phoronis 

 when it is twelve hours old possesses both the recipient and distribut- 

 ing vessels; these vessels, I believe, arise by the fusion of the walls of 



Fig. 3. Transverse section through the anterior region of dJi Actinotrocha which has 



just completed its metamorphosis. X 360. d.v^ dorsal blood vessel (afferent blood 



vessel); v.v, ventral blood vessel (efferent blood vessel); r, rectum ; e/.S, branches of 



efferent vessel which are continued into the recipient vessel of the adult. 



the single ring-vessel in the metamorphosing Actinotrocha and by the 

 subsequent seperation of the two parts along the line of fusion. 



Blood Corpuscles: The red blood corpuscles of the adult Pho- 

 ronis make their appearance in the young Actinotrocha and when the 

 latter becomes fully developed, they are usually present as one or two 

 pairs (according to the species) of conspicuous red masses in the larval 

 collar-cavity (Fig. 2 h.c). 



All the earlier observers describe these masses of blood corpuscles 

 but E. B. Wilson is the first to discuss their origin. According to his 

 view, they develop in solid masses, adhering to the stomach wall -near 

 the base of the tentacles. 



Caldwell'^ tells us in a general way that the blood corpuscles 



1 Proe. of the Eoy. Soc. Vol. 34. 1882, 1883. 



