240 THE STRUCTURE AND- AFFINITIES OF HERDMANIA CLAVIFORMIS. 



Branchial Sac. Without folds or internal longitudinal vessels; membranes 

 of transverse vessels and dorsal languets present; stigmata straight, simple (Fig. 3). 



Neural gland situated on ventral side of cerebral ganglion (Fig. 5), provided with 

 a long rapheal duct. 



Digestive Tract. Loop of intestine straight, very long, the oesophagus constitut- 

 ing one of the limbs; stomach wall deeply fluted (Fig. 2). 



Genitalia. Ovary situated some distance behind the intestinal loop, oviduct 

 serving as a uterus in which the embryos go through their development to nearly the period 

 of metamorphosis (Fig. 2). Testis in the form of numerous lobes which may extend 

 from the intestinal loop to a considerable distance behind the ovary. 



Heart. Situated in the postabdomen behind the ovary (Fig. 2). 



Epicardiac Tubes. Two, separate throughout their length. 



III. DETAILED DESCRIPTION OF HERDMANIA. 



i. General Character of the Colony. — Although the ascidiozooids are never 

 enveloped in a common test, they usually arise very close to one another from the 

 much-branched stolon, and are consequently closely crowded in the colony. The 

 colonies are of considerable size, their area frequently covering 100 to 200 square 

 centimetres. More frequently than otherwise a considerable quantity of sand and 

 detritus is spread over the colonies, and this usually adheres more or less to the test. 

 The zooids are often buried for half their length in these foreign substances. The 

 colonies are found on rocks more commonly than on other objects. Their most usual 

 position is the upper surfaces of the rocks among the roots of various seaweeds. The 

 bathymetric range of the species appears to be quite restricted. It rarely if ever 

 occurs much above extreme low tide, and it has never yet been taken with the dredge. 

 The fact must be borne in mind, however, that the dredge is a very inadequate means 

 for exploring rocky bottoms. It has not yet been taken north of Half -moon Bay, 

 California, or south of San Pedro. It is an abundant species at most points through- 

 out its range, though perhaps most so in Monterey Bay. 



2. Ascidiozooids. — These are long and slender and distinctly thicker at the an- 

 terior than at the posterior end. The average length is about 20 millimetres, though 

 exceptional individuals may reach twice this length. The anterior, larger end, the 

 thorax, is somewhat compressed laterally. Its greatest diameter is about 4 milli- 

 metres. The body is not set off into distinct regions, although an obvious diminution 

 in the dorso-ventral diameter occurs at the posterior end of the thorax. From this 

 point back the body is circular in section and narrows gradually to its junction with 



