8 E. w. MAC-BRIDE AND j. c. SIMPSON. 



and a second brood dredged a fortnight later, are of approximately identical 

 development. These embryos all measure from 2 5 to 3 mm. in length, and have 

 assumed the typical ten-tentacled form. The tentacles are still simple, unbranched, 

 peg-like outgrowths (Fig. 6), but there is some slight indication of a differentiation in 

 size, the two ventral tentacles being just a shade smaller than the rest. 



In sections the digestive tract is seen to be well developed, though the ossophagus 

 is still solid, and the anus has not yet been formed. The stomach walls are thrown 

 into heavy folds and the intestine shows the characteristic double twist. 



The water-vascular system in this stage shows many advances. The pore-canal 

 can be distinctly seen to open to the outside, and can be traced into the axial sinus, 

 which runs for a short distance in the body-wall before it communicates with the stone- 

 canal. The presence in Holothurians of an axial sinus opening, on the one hand, into 

 the stone-canal, and on the other to the outside by means of the pore-canal, has been 

 described in two cases only once by Bury (2) and once by Ludwig (6). As Bury's 

 observation, however, has been very generally questioned, and as Ludwig, though 

 noting the presence of these structures, does not attach any very great weight to them, 

 the present discovery becomes of extreme interest and importance, as a confirmation 

 which places the matter beyond doubt. As has been noted above, in the younger 

 embryos the pore-canal cannot be traced throughout its whole length, but this is in all 

 probability due to bad preservation. 



A large Polian vesicle is now seen in the left dorsal interradius, a position which 

 Ludwig (5) says it occupies in some Cucumarise, though he does not mention C. crocea. 

 Tube feet have made their appearance, and we now find four arising from each radial 

 canal, though they have not as yet reached the surface. 



The state of the preservation prevents any very minute study of the nervous 

 system, but one can readily see the well-developed nerve-ring and the five radial 

 nerves, as well as the branches to the tentacles. 



The epi-neural ring and canals are also clearly seen, and we find that the ring also 

 gives off branches which accompany the tentacular nerves. 



Of the condition of the mesenteries little can be made out. A bunch of cells in 

 the dorsal mesentery close to the stone-canal may very possibly be the rudimentary 

 gonad, but of these points it is impossible to be sure. 



In conclusion, it may be said that the collection, though small, has yielded many 

 interesting points. Chief among these may be mentioned the discovery of two 

 pelagic Echinoderm larvae within the Antarctic Circle, and of the brood-pouch in 

 Cucumaria crocea. The first are important because they disprove the generally 

 accepted theory that none ot the Antarctic Echinoderms have free-swimming larvae, 

 the second because it fills a gap in our knowledge of the life-history of a well-known 

 form. The well-marked axial sinus and pore-canal in the Cucumaria embryo is also 



