92 Papers from the Marine Biological Laboratory at Tortugas. 



Each colony contains several parasitic ainphipods. 



In some parts of the colony the ascidiozooids are arranged in regular, 

 circular systems of 5 to 6. In other parts no distinct systems are visible. 

 The ascidiozooids are large, reaching 5 to 6 mm. in length. They are 

 rather closely placed and lie at right angles to the surface. 



The preserved specimens are of course more or less contracted. 

 In one colony, I found an abdomen apparently very little if at all con- 

 tracted, measuring 9 mm. (fig. 3). In the living condition ascidiozooids 

 may therefore reach 12 mm. or more in length. 



The abdomen is about three or four times as long as the thorax. 

 From the posterior end of the abdomen or from the ventral side near 

 the posterior end one or, more rarely, two ectodermal processes (vas- 

 cular appendages) are usually given off (fig. 5), which vary in length 

 and sometimes are wholly wanting. The siphons are well developed, 

 provided with strong musculature, and both 6-lobed. They are of equal 

 length or the atrial siphon is a little longer than the branchial siphon. 

 The branchial sac was very much contracted. There are only three 

 rows of long, narrow stigmata. 



The alimentary canal forms a very long and narrow loop and is 

 not twisted (fig. 2). The oesophagus and intestine are both very long 

 and straight. The stomach is smooth-walled and situated near the 

 posterior end of the abdomen in the long axis of the body. In somewhat 

 contracted specimens it is heart-shaped or nearly globular in outline 

 (figs. 2,4); in others which were not contracted it is of ellipsoidal or 

 fusiform shape (fig. 3). Leaving the stomach the intestine bends dorsally 

 for a short length and then extends straight anteriorly. The rectum 

 lies along the oesophagus on the left side, and is partly covered by it 

 (fig. 2). In some ascidiozooids the course of the alimentary canal was 

 somewhat different. The stomach was situated on the dorsal side; the 

 intestine leaving the stomach turned first ventrally and then backward 

 dorsally, passing the stomach on the left side (fig. 4). Intestine and 

 rectum contained several fecal pellets. 



The testes were developed in only some of the ascidiozooids. They 

 are pyriform and very numerous, 30 to 40 in number, situated near the 

 posterior part of the stomach (fig. 4) or covering the right side of the 

 stomach (fig. 6). None of the specimens examined contained eggs or 

 embryos. 



Polycitor mayeri is one of the largest and most beautiful species of 

 the genus Polycitor. On account of the number of the rows of stigmata 

 and the smooth-walled stomach it belongs to the subgenus Eudistoma 

 Caull. It seems to come nearer to Polycitor {Eudistoma) mucosum 

 Drasche, from the Mediterranean, than to any other species of the genus, 

 but differs from it in shape and color of the colony as well as in the length 

 and some other anatomical details of the ascidiozooids, so that it is 

 doubtless a distinct and well-marked species. It is not only the first- 

 known Polycitor from the West Indies, but from the whole eastern coast 

 of the American continent. 



From the western Atlantic only five species of this genus have been 

 described, and all of these are mentioned b}^ Van Name from the Ber- 



