MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 105 



pear and ovaries begin to develop about the. first of May. While this is going on, individuals 

 which were born later in the summer of the year before begin t<> develop testes and lophophoral 

 organs, and thus we have individuals with lophophoral organs and testes occurring at the same 

 time of the year as individuals without lophophoral organs and with ovaries. 



While there is do absolute proof, the upper part at least of the lophophoral organs prob- 

 ably functions as a kind of seminal receptacle. We are led to this conclusion by these facts: 

 First, that the organs appear only when the testes are present; second, that large bunches of 

 spermatozoa have been found in the body cavity, in the nephridia, and in the cavitj* of the lopho- 

 phoral organs; and, third, that there are ciliated grooves leading from the nephridial pores to the 

 cavities of the lophophoral organs. 



Vascular system. Nearly all of the early investigators of the anatomy of Phoronis recognize 

 the existence of an efferent and afferent vessel which are in connection with vessels running up 

 into the tentacles. 



Caldwell's (3) description, although brief, is complete, and differs very little from later ones. 

 Cori's (-1) account seems to be about the same as Caldwell's; however, he recognizes one ring 

 vessel instead of two and describes in more detail the relation between the tentacular vessels and 

 the ring vessel. 



In Phoronis austral/is, Benham (2) finds the circulatory system much the same as Caldwell 

 does in the form that he worked on. Practically the only point of difference is that he describes 

 the tentacular vessels as dividing into two branches, one opening into the distributing vessel 

 (inner) and the other into the recipient vessel (outer). 



Andrews (1) finds that the vascular system of P. architecta, as far as he has determined, is 

 like that of /'. australis, while Ikeda (9) says that Benham's description holds good for /'. ijimai 

 and P. hippocrepia. 



A transverse section through the lophophoral crown of /'. arvhitecta (fig. 63) shows that the 

 cavity of each tentacle contains a blood vessel which is attached to the inner surface of the wall. 



At the base of the tentacles a cross section shows that there are two blood vessels running 

 parallel to one another through most of their course around the cavity of the lophophore (tigs. 65 

 to 71). These vessels are distinct, although closely applied to one another, thus differing from 

 what Cori finds in /'. psammophila. The outer vessel and inner vessel (figs. 65, 66) are, respec- 

 tively, the "recipient" and " distributing" vessels which Benham describes. In tig. 83 is shown 

 a ci'o-s section through the base of the tentacles. Throughout most of the section the tentacular 

 vessels open into the outer or recipient vessel, but at one end the tentacular vessels open into 

 the inner or distributing vessel. This section, together with sections anterior and posterior to 

 it, show conclusively that the tentacular vessel has two separate openings, one into the distribu- 

 ting vessel, the other into the recipient vessel, and that the distributing and recipient vessels are 

 completely separate. A longitudinal section through the anterior end of Phoronis architecta 

 shows conclusively that the tentacular vessel divides into two branches, one opening into the 

 recipient vessel and the other into the distributing vessel. 



A little moi - e posteriorly the ring-like distributing vessel opens into a median longitudinal 

 vessel lying between the oesophagus and rectum but close to the wall of the former (tigs. 67, 68). 

 This vessel, which is the afferent vessel, pierces the transverse septum (tig. 69) and runs 

 posteriori}* (within the rectal or posterior chamber) between the two arms of the alimentary 

 canal. At the point where the vessel passes through the septum there is a thick layer of muscle 

 fibres surrounding flic former which undoubtedly has the power of shutting off the blood supplj 

 to the tentacles and which may be very necessary to prevent the animal from bleeding to death 

 when the lophophoral crown is cast away (tigs. 68 to 71). 



The two sides of the ring-like recipient vessel do not pass into a single vessel while they are 

 within the supraseptal cavitj (tigs. ti7 to 71), but after they have pierced the transverse septum 

 the right side of the ring is seen to pass diagonally across the (esophagus and to meet the left 



side of the ring (figs. 75 to 7S). From this point the two becom< vessel, the efferent vessel, 



which runs posteriorly within the left body cavity. In the posterior part of the body, where 

 the alimentary canal makes a loop, the efferent and afferent vessels are continuous and open into 



