REPORT ON THE TUNICATA. 



27 



animal in the reverse position to that employed by most authors, that is, he has the base 

 of attachment upwards, and the branchial aperture hanging down. These are his superior 

 and inferior regions ; then the endostyle is placed forwards and called anterior, while the 

 opposite edge — the atrial part — is posterior. The result is that the stomach lies on what 

 Lacaze-Duthiers considers the right side of the branchial sac — the same arrangement as 

 was obtained by the systems of Savigny and Hancock, although the last mentioned 

 authors placed the animal so that the branchial aperture should be superior (see diagrams 

 in Lacaze-Duthiers' memoir). 



Julin, 1 and apparently Traustedt 2 also, employ the same nomenclature as Heller, and 

 this is the system adopted in the present work. If the animal be placed with the endostyle 

 downwards, and the branchial aperture pointing away from the observer, then the two sides 

 correspond with his right and left hands. The region of the branchial aperture (fig. 1, Br.) 



Fig. 1. — Diagram showing the position of an Ascidian, viewed from the left side. 



A., anterior end ; P., posterior end ; D., dorsal edge ; I'., ventral edge ; Br., branchial aperture ; At, atrial aperture ; br.s., branchial 

 sac ; en., endostyle ; <e.a., oesophageal aperture ; St., stomach ; i., intestine ; a., anus ; n.g., nerve ganglion. 



is thus anterior, and the opposite end, usually the place of attachment, is posterior ; the 

 lower surface, along which the endostyle {en.) runs, is ventral, and the opposite edge, on 

 some part of which the atrial aperture generally opens, is dorsal. 



According to this system, the stomach (st.) and intestine lie (in most of the genera 

 and species of Simple Ascidians, e.g., Ascidia mentula) upon the left side of the branchial 

 sac (fig. 1) and this side corresponds to the left side of Milne-Edwards, Kupffer, Heller, 

 Hertwio-, Traustedt, and Julin, but to the right side of Savigny, Alder, Hancock, Lacaze- 

 Duthiers, &c. 



1 Recherches sur rOrganisation ties Ascidies Simples, Arrh. ' U . vol. ii. p. . r >9. 



5 Oversi^t over de fra Danmark, &c, Asc Simp., Vid. Maid. Nat. For. Kjfbenluimi, 1879-SO. 



(ZOOL. CHALL. EXP. — PART XVII —1882.) E 5 



