36 DISCOVERY REPORTS 



white area on each side of the body wall near the base of the ventral part of the thorax (Fig. 3 E, tri.). 



Other specimens have no trace of this (Fig. 3 C). 



Gut. The oesophagus is usually longer than the stomach and is widest at its branchial end. There 

 is much variation in the stomach. The zooids of some colonies have a stomach with five to seven 

 shallow but distinct longitudinal folds (Text-fig. 3 C), but in other specimens (Text-fig. 3 E, F, G) the 

 folds are reduced to a variable degree, or broken up into a few indistinct swellings or completely 

 absent. In the last case the stomach is like that of Synoicwn. The intestine and rectum are of the type 

 usual in Aplidium. The anus has two small diverging lips ; it is situated opposite the 9th row of stigmata 

 when twelve rows are present and opposite the 12th row in zooids with twenty-one rows. 



Gonads. The ovary is either close behind the intestinal loop (Text-fig. 3E, ov.) or at some distance 

 from it (Text-fig. 3 C, ov.). A long series of small testis follicles (t) occupies much of the length of 

 the post-abdomen. 



Larva (Text-figs. 3 D, H). The trunk of the larva ranges in length from 0-40 to 0-70 mm. The three 

 papillae are closely spaced and are borne on slender stalks. There are four long narrow median ampullae 

 and four pairs of shorter stouter lateral ampullae. On each side of the dorsal and ventral part of the 

 trunk there is a slender strand of tissue bearing a series of small rounded vesicles (ves.). Both ocellus 

 and otolith are present. 



Larva 



Slender. Trunk 0-40-0-70 mm. 

 Papillae close. Lateral series of 

 dorsal and ventral vesicles 



Stout. Trunk o-6 — 0-90 mm. Papil- 

 lae distant. No series of vesicles 



Biology. Colonies were collected in all months of the year except August and September, and 

 larvae were found in the subantarctic material in January, February, March, April, June, July, 

 October, November and December. There were no larvae in the antarctic specimens. It appears that 

 the species breeds throughout the year, and in this respect resembles A. caeruleum as described by 

 Hartmeyer (191 1). The larvae in each breeding zooid number from four to nine. 



None of the colonies showed the accumulation of reserve material in the post-abdomen which is 

 commonly found during the post-breeding and overwintering period in many species of polyclinid 

 ascidians. It may be that in species which breed almost continuously throughout the year the de- 

 differentiation of zooids and the accompanying resting phase have been reduced. 



Remarks. I have been surprised that this species, which is apparently common round the Falkland 

 Islands and on the Patagonian Shelf, could not be identified with any known species, and I suspect 

 that hitherto it has been confused with A. fuegiense, with which it is often collected. A comparison 

 of the two species is shown in Table 7. 



It is evident from the table that the larva affords the best characters for distinguishing the species, 

 as will be seen also by comparing Text-figs. 2 A 1 and 3D, H. 



The larva also indicates that specimens possessing white thoracic triangles and those lacking them 

 are both of A. falklandicum (see Text-figs. 3 D, H). It unites, too, a whole series of specimens showing 

 structural differences in the stomach, which might otherwise have been thought to indicate specific 

 differences. 



Distribution. Subantarctic (Falkland Islands, Patagonian Shelf); Antarctic (Graham Land, 

 S. Orkneys, S. Georgia). 





