REPORT ON THE TUNICATA. 125 



In Culeolus recumbens the dorsal part of the intestine or rectum is short compared with 

 the ventral part next the stomach ; this is caused by the atrial aperture being situated on 

 the dorsal edge, and not at the posterior end of the body. In Culeolus mwrrayi, where 

 the atrial aperture is more posterior, the rectum is longer. In Culeolus perlucidus, where 

 the atrial aperture is not quite posterior, the great length of the rectum is caused by its 

 devious course. 



The form and course of the alimentary canal in the genus are thus very similar to 

 what is found in the majority of Simple Ascidians, and may easily be derived from the 

 arrangement found in the genus Ascidia (fig. 15, left hand diagram) by twisting the 

 rectum round posteriorly, so as to allow the anus to follow the atrial aperture from the 

 anterior to the posterior end of the dorsal edge. 



Ascidia. Cufrohtn. 



Fig. 15. — Diagrams of Ascidia and Culeolus, seen from the right side, to show the course of the Alimentary Canal. 



Br., branchial aperture ; At., atrial aperture ; ped., peduncle ; In., tentacles ; d.l., dorsal lamina ; ce.a., cesophageal aperture ; 



St., stomach ; i., intestine ; a., anus ; 1, intestinal loop ; 2, rectal loop. 



Thus the rectal loop, or second intestinal curve (2), concave anteriorly in Ascidia, is 

 entirely done away with in Culeolus (fig. 15, right hand diagram). In Culeolus 

 perlucidus there is a rudiment of it, as the rectum is long, and, after running rather 

 farther posteriorly and ventrally than the atrial aperture, has to curve up again dorsally, 

 so as to bring the anus near it. If we compare this arrangement with that found in a 

 species of Ascidia where the atrial aperture is placed far back on the dorsal edge, as in 

 Ascidia depressa, the difference will appear very slight. 



The course of the intestine in Culeolus mwrrayi, where the atrial aperture is posterior 

 and the rectum runs straight towards it, is the simplest, and seems probably to have 

 been the archaic form. Culeolus perlucidus has the atrial aperture rather more dorsal in 

 position, and consequently there is a slight twist upwards in the terminal part of the 

 rectum. Ascidia is a still more modified form in which the atrial aperture is normally al 

 the anterior cud of the dorsal edge, and here we find the rectal loop fully developed and 

 the rectum running anteriorly in place of posteriorly as in Culeolus. 



The Genitalia. The genital glands, like the intestine, could only be examined in the 

 three species of which there are more than single specimens. 



