38 DISCOVERY REPORTS 



the lower end of the colony merely being flat. The head of the stalked colonies is almost spherical, or 

 ovoid or cylindrical. The general colour of the preserved colony is grey, patterned by the regular 

 double rows of zooids, converging at the apex of the colony, which constitute one of the most charact- 

 eristic features of the species. The double rows are produced by the adjacent long narrow oval systems 

 of zooids. Each of the systems has a long central cloacal canal, and the canals of most of the systems 

 open into a common depression at the apex of the colony. Although this is the condition generally 

 found in the species, some colonies have, in addition, other cloacal openings scattered over the surface, 

 as observed by Kott (1954). Sand is almost always present within the common test, especially in the 

 superficial layers, but the test material itself is transparent. The largest and smallest specimens in the 

 collection are 6-4 and 1-5 cm. in total length. 



Zooid (Text-fig. 4 A). The zooid is large and stout, the thorax being about 3 mm. long and the 

 abdomen about the same length; the post-abdomen is variable, and often exceeds the combined 

 length of the thorax and abdomen. 



Thorax. The three narrow pointed lobes of the atrial languet (a.l.) are always present. Sluiter 

 (1906) noted that the atrial opening is placed a short distance back on the dorsal side of the thorax. 

 The ' Discovery ' specimens not only confirm this as a constant feature of the species, but also show 

 that in all well-expanded zooids the opening is of a size unusually great in Aplidium, and exposes a 

 large part of the dorsal side of the thorax (a.o.). There are thirteen to nineteen rows of stigmata, the 

 number being independent of the size of the colony, at least in the ' Discovery ' specimens, all of 

 which are well grown. 



Gut. The oesophagus varies in length. According to Sluiter (1906) and Kott (1954) the stomach has 

 four longitudinal folds, but I find a considerable variation in the appearance of the stomach in zooids 

 even from the same colony. In many there are six to eight folds (Text-fig. 4B), but other zooids have 

 a stomach showing no true folds. One or other of these conditions is probably an artifact. The folds, 

 when present, are rather shallow in the 'Discovery' specimens. The undivided anus lies between the 

 8th and 9th rows of stigmata in zooids with 13 rows. 



Gonads. In some colonies zooids were seen with an ovary and in others there was a very slightly 

 developed testis (t) in the form of a row of small pear-shaped follicles. 



Biology. There is not enough material to give much information on this subject. One specimen 

 taken in March (St. 190) had large eggs in the oviduct and one specimen in the same month (St. 27) 

 had embryos in the atrial cavity, but larvae were not found in any colony. Kott (1954) recorded 

 embryos in January in her specimens from the neighbourhood of Enderby Land, but unfortunately 

 they too were not fully developed. The embryos are very large, according to Kott. 



Remarks. Some of the ' Discovery ' specimens were taken from near the type locality in the Palmer 

 Archipelago, but others extend the known range of the species to the South Orkneys and South 

 Georgia. 



This species has two features unusual in the genus: (1) sharp division of the colony into a head 

 which carries the oral and cloacal openings and a stalk which lacks them; and (2) the openings of 

 cloacal canals from several systems into a common apical depression. 



These are both characters found elsewhere principally in species of Sycozoa. 



Distribution. Western Antarctic (Graham Land, South Orkneys, South Georgia), Eastern 

 Antarctic (Enderby Land). 





