REPORT ON PHORONIS BUSKII. 17 



oesophagus, stomach, and intestine. Similar food occurred in the canal of the Australian 

 Phoronis, though there Vas a greater abundance of muddy debris. 



Dr. Strethill "Wright considered that the alimentary system of Plwronis resembled 

 that in Plumatella, the mouth being placed within the tentacular ring and closed by a 

 semicircular lip or valve. In the new form the oral aperture is closed by simple 

 approximation of the surfaces, as the very short free margin can hardly be taken into 

 account functionally. Wright describes the long gullet as terminating in a gizzard the 

 interior of which was provided with bodies apparently cartilaginous and of a prismatic 

 shape. The gizzard communicated with a thick-walled stomach. He probably refers 

 to the massive folds of the mucous surface, as no hard parts occur in the canal. He 

 did not follow the intestine minutely, but he noticed a membranous tube containing 

 fusiform faeces passing to the anus, whence they were often ejected. 



Kowalewsky describes the alimentary canal in Phoronis as built up on the same 

 plan as in Ascidia,^ the first opening in the embryo being the anus, and the mouth 

 appearing subsequently. The same author mentions that the alimentary canal is 

 suspended by a mesentery. Caldwell, again, derives the anus as well as the mouth 

 from the blastopore, the remnant of the primitive streak — the posterior solid cord of 

 cells — opening up and forming a canal leading from the archenteron to the exterior. 



Circulatory Organs. 



The chief point observable in regard to the circulatory organs in the preparations 

 is the presence of the great dorsal trunk, which extends almost, but not quite, from the 

 posterior to the anterior end of the body along the posterior (or dorsal) arch of the 

 alimentary canal in the groove between the intestinal mesenteries. In the anterior or 

 contracted region of the body rupture of this vessel frequently occurs, the contents pass- 

 ing laterally, so as to simulate a second vessel. On the right of this region, and not on 

 the anterior or ventral surface, the other great trunk proceeds. The dorsal trunk 

 terminates in the great sinus in the anterior body-cavity (PL II. fig. 1), and thence the 

 vessels to the branchi^ go forward. Many large branches occur in the spaces between 

 the alimentary canal and the ]>ody-waU, and are very conspicuous in the interstices of 

 the radiate fibres in the anterior region, and at the tip of the tail after the great 

 dorsal and lateral trunks disappear. They are especially abundant in connection with 

 the reproductive organs, as Kowalewsky and others noticed. Many small vessels are 

 apparent beneath the primary divisions of the alimentary canal, but no large trunk 

 occurs in that position. None of the vessels are so small as to merit the name of 

 capillaries, and all are loaded with large circular nucleated cells. 



In the living form Dr. Strethill Wright observed an artery passing forward in the 

 axis of the body close to the gullet till it reached the concave side of the tentacular 



1 Entwicklungeschichte d. einfachen Ascidien, note, p. 5, Mem. Acad. imp&. .St. Petersl., t. x. 



(ZOOL. CHALL. EXT. PART LXXV. — 1888.) ffff 3 



