124 



Mr. A. E. Shipley. 



[May 16, 



This tissue forms a ring in the lower lip, external to the vascular 

 spaces in this region ; it also sends extensions into the tentacles. It 

 seems to support and stiffen these structures, and from its position 

 serves as a firm hold for the insertion of the retractor muscles of the 

 introvert, which are attached just behind it. 



The Alimentary Canal. — The oesophagus is lined with ciliated 

 epithelium, continuous with that of the lower lip and the tentacles. 

 Its cavity is diminished by numerous ridges, the grooves between 

 which are continuous with the grooves on the tentacles. The intes- 

 tine forms about fifteen coils ; it is usually full of fine sand, and 

 appears to be partly ciliated, though there is no ciliated groove as in 

 Sipunculus. The rectum is straight, and its cavity is also occluded 

 by ridges. The anus is surrounded both by a sphincter muscle and by 

 a number of radiating fibres. 



The Vascular System. — There are two kinds of blood corpuscles 

 present in Phymosoma. The larger kind occurs in the body cavity : 

 they are oval in outline, with a spherical nucleus. The smaller kind 

 is found in a closed series of spaces usually termed the vascular 

 system. This space may be described as consisting of three parts, all 

 communicating with one another. The first of these lies in the lower 

 lip, and consists of a number of channels anastomosing with one 

 another, the interspaces being occupied by the skeletal tissue described 

 above. These channels open at their dorsal ends into the second 

 series, which forms a space at the base of the lophophore. This gives 

 off a number of spaces, which pass into the tentacles and open in the 

 middle ventral line into the dorsal vessel. This is a muscular sac 

 which is attached to the dorsal surface of the oesophagus between the 

 retractor muscles of the right and left side. It serves as a reservoir, 

 into which the corpusculated fluid is driven when the introvert is 

 retracted and the tentacles are flaccid. By the contraction of its wall 

 the blood is forced into the lower lip and lophophore, and these 

 organs are then dilated. The whole is lined by a flat epithelium. 



The Nephridia. — Each nephridium consists of two parts, the bladder 

 and the true secreting part. Both these parts are well supplied with 

 muscle fibres and are consequently very contractile, so that their 

 shape varies greatly in different specimens. The bladder, which is 

 the anterior half, is attached to the body wall by mesenteries, the 

 secreting part is free. The bladder opens to the exterior by a circular 

 mouth, and to the interior or body cavity by a ciliated opening in 

 shape like a flattened funnel. The lumen of the secretory part is 

 broken up into a number of side chambers, which may be readily 

 described by comparing them to the air-chambers in the interior of a 

 frog's lung. The whole is lined by a very peculiar epithelium. The 

 cells composing this are columnar in shape, with their nuclei at the 

 base. They are crowded with minute spherical granules, and many 



