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its mesodermal covering and blood corpuscles are carried back and 

 forth from it to the sinus by the contraction and expansion of the 

 former. Anteriorly the dorsal vessel can plainly be seen opening into 

 the ring- vessel (larval collar-cavity). 



The origin of the connection between the dorsal vessel and the 

 ring-vessel and the manner in which the blood corpuscles find their 

 way into the former are questions which have not been very satisfac- 

 torily elucidated. To my mind, the Actinotrochae from Beaufort 

 Harbor present no great difficulties in the way of understanding how 

 these processes take place. The dorsal blood vessel opens posteriorly 

 into the sac-like sinus around the loop of the alimentary canal and it 

 seems probable from an examination of sections of the critical stage 

 that it is also open anteriorly. Assuming that such is the condition, 

 it will open into the space between the mesodermal lining and the 

 wall of the gut. This space, however, is in free communication with 

 the larval collar-cavity (adult ring-vessel) which contains the blood 

 corpuscles. Under these conditions the blood corpuscles can pass into 

 the dorsal blood vessel from either end. 



Shortly after the critical point in the metamorphosis, the mesoder- 

 mal lining on the left side of the oral limb of the " Z7" shaped alimen- 

 tary canal begins to show indications of becoming a blood vessel and 

 when the metamorphosis is completed, a definite vessel (Fig. 3 e.f) is 

 seen which opens posteriorly into the spacious blood sinus around the 

 loop of the alimentary canal. Anteriorly before reaching the transverse 

 septum, it divides into two branches which run obliquely upward 

 along the sides of the alimentary canal almost encircling the same; 

 these finally open into the ring-vessel of the supraseptal cavity. The 

 vessel described becomes the efferent vessel of the adult and its 

 branches become part of the recipient vessel (Fig. 3). 



Above it is stated that I believe the stage in the development of 

 the blood vessels which Masterman and Roule describe for the 

 Actinotrocha corresponds to the stage which is found in the metamor- 

 phosed Actinotrocha from Beaufort Harbor. These two observers 

 recognize a ventral blood vessel along the stomach but such a structure 

 is not present in the Beaufort Actinotrocha. It, however, makes its 

 appearance just after metamorphosis and is undoubtedly the same as 

 the efferent vessel of the adult which has just been described. 



Masterman also speaks of a "ring-sinus" connecting the dorsal 

 vessel with the ventral vessel at the posterior end of the stomach and 

 a "postoral ring-sinus" which does the same at the anterior end of the 

 stomach. The former is undoubtedly identical with the spacious blood 

 sinus, which has been described above, as surrounding the loop of the 



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