AETEA 473 



figure is, I think, due to the omission of the nearer calcareous wall of the head of the 

 zooecium, which would have been visible at a higher focus. In my material the cells are 

 more closely packed, but an embryo with loosely packed, rounded cells, as in that figure, 

 might be found at a different stage of segmentation. 



Marcus (1937, p. 28) made the suggestion, warranted by the figure, that the structures 

 seen by Robertson were algae such as he had found attached to his own material in 

 various positions. The contents of the sacs in my specimens are certainly animal 

 embryos, though I do not know whether they are Polyzoan. It is, however, worth 

 noticing that the most advanced embryo resembles many Polyzoan larvae in shape 

 (Fig. 57 B). Despite his suggestion that Robertson's ovisacs were algae Marcus later 

 (1938 b) regarded the form with frontal ovisacs as a distinct species, but the very close 

 agreement in other characters seems to preclude this separation. 



Examination of zooecia stained with borax carmine (without decalcification) and 

 mounted in canada balsam has shown me beyond doubt that the spots on the walls are 

 pores, as described by Levinsen, not protuberances. The examination of the optical 

 section of the wall as seen at the periphery of a profile view proves this, for the fine 

 tubes or passages can be seen, corresponding to the dots and passing through the thick- 

 ness of the wall at right angles to the surface. Moreover, examination of the annulated 

 part in optical section shows which of the alternating rings are calcareous and which 

 not, the calcareous ones being thicker in section. The calcareous rings have a slightly 

 more opaque, greyer appearance than the non-calcareous ones, and they exactly match 

 the wall between the dots in colour and texture. The fusion of dots to form linear marks 

 and then rings, as described by Marcus, is to be seen, but the rings so formed are the 

 non-calcareous ones, as might be expected from the fusion of pores. 



2. Aetea curta Jullien. Plate XIII, fig. 1 ; Fig. 58 A, B. 



Aetea curta Jullien, 1888, p. 26. 



? Aetea truncata Marcus, 1938a, p. n, pi. i, fig. 4. 



Station distribution. Ascension Island: St. 1. 



Geographical distribution. Magellanic Region (Jullien); Brazil? (Marcus); Ascension Island 

 (Discovery). 



A specimen of Aetea from Ascension Island has zooecia in which the erect part is 

 shorter than the encrusting part, and the opesia nearly always occupies more than half 

 the length of the erect part (Fig. 58 A, B). The encrusting part tapers at the proximal 

 end, but for at least half its length it is dilated and wider than the erect part. The erect 

 part is relatively of very uniform width, and may be somewhat curved. The surface of 

 the zooecia is very finely punctate almost throughout, only the extreme proximal end 

 of the encrusting part appearing smooth. In this species, as in A. anguina, the puncta- 

 tions are pores. This is particularly clearly seen at the broken edge of a piece of the wall 

 mounted in balsam, and can also be deduced from the appearance of the optical section 

 of the wall seen at the periphery of mounted specimens. The pores are much smaller 

 than those of A. anguina. In addition to the pores the encrusting part and the tubular 



