1884.] Balanoglossus Kowalevskii (Agassiz), Sfc 23 



horizon, relative to those of the British Basalts, and their floras do 

 bear a resemblance to some of those said to be Miocene of Central 

 Enrope ; but as for the Greenland plants brought home by Whymper 

 and by Golomb, they have no Miocene characters whatever, and there 

 should be no hesitation in referring them to the same ages as the 

 Basaltic floras of our own country. 



II. "Note on the Later Stages in the Development of Balano- 

 glossus Kowalevskii (Agassiz), and on the Affinities of the 

 Enteropneusta." By William Bateson, B.A., Scholar of 

 St. John's College, Cambridge. Communicated by Pro- 

 fessor Michael Foster, Sec. R.S. Received December 4, 

 1884. 



In the " Quart. Journ. Micr. Sci.," vol. xxiv, n.s., p. 208, I described 

 the embryonic stages in the development, of a small species of Balano- 

 glossus which is found on the American coast. By a direct embryonic 

 development, this animal reaches the condition in which one pair of 

 gill-slits is present, no " Tornaria " stage being passed through. I 

 have since had an opportunity of observing the further development 

 of this form until it becomes a mature animal possessing from 

 thirteen to forty pairs of gill-slits. The remarks which follow 

 contain a preliminary account of the steps by which this condition 

 is reached. 



At the time of hatching, the body of the animal consists of four 

 regions: (1) a conical proboscis bearing at its apex a tuft of long 

 cilia ; (2) a very short collar-region ; followed by (3) a dilatation 

 of the body, in the dorso-lateral regions of which a pair of gill- 

 openings soon appear. Immediately behind these gill- slits is a 

 transverse ring of cilia, which separates the third region from (4) the 

 anal region. The opening of the mouth is still ventrally directed, 

 and the anus opens at the dorsal side of the posterior surface in the 

 middle line. 



The following are the external changes which then occur : — 

 (1.) The transverse ring of cilia disappears, being absent in larvae 

 possessing two pairs of gill-slits. The apical tuft of cilia also dis- 

 appears. The cilia which cover the whole body increase in size, and 

 unicellular glands appear in the skin, especially of the proboscis, 

 giving it a speckled appearance. The tissues become gradually more 

 transparent, presumably from the consumption of the yolk particles 

 with which the cells had previously been filled. 



(2.) As the cilia disappear, a remarkable temporary organ aonears 

 in the form of a conical process, or tail, arising from the posterior 



