472 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



Fig. 7 represents from the left side a slightly later stage 

 in which the stomodaeal invagination has met and opened 

 into the hitherto blind end of the archenteron. The three 

 divisions of the gut — oesophagus (oes.), stomach (st.), 

 and intestine (int.) are now well denned. Communication 

 between the left coelomic vesicle and the exterior is 

 established by a tubular outgrowth — the pore-canal (p.c.) 

 — from the vesicle, which meets and fuses with an 

 invagination from the dorsal wall of the larva. The 

 invagination becomes perforate, and forms the madreporic 

 pore (m.p.). The same organs are seen in fig. 6, which is 

 a ventral view of a slightly older larva. Here the pre- 

 oral and post-oral portions of the ciliated band (c. b.) also 

 are clearly defined. In fig.. 8, a still later stage, the whole 

 of the ciliated band is defined, and the pre-oral lobe 

 (pr.o.l.) has assumed its characteristic shape. The 

 stomach is now large and subglobular. Both coelomic 

 vesicles, the left (I.e.) much the larger, are beginning to 

 grow forward in the direction of the pre-oral lobe. In 

 fig. 9, the latest stage of this larva which I have been 

 able to -trace with certainty, this forward growth has 

 proceeded much further, and the posterior portions of the 

 vesicles have begun to envelop the stomach. The walls 

 of the vesicles are now much thinner, and, except in 

 the living larva, are traced with difficulty. Field (1) 

 discusses at some length the occurrence of a right hydro- 

 coel in some of the larvae of Asterias vulgaris studied by 

 him. Gemmill (4) has recently shown that this 

 interesting feature occasionally occurs in the larvae of 

 Asterias rubens and A. glacialis, and (5) in that of 

 Porania 'pulvillus. I have not observed it in the larva 

 just noticed. 



In a recently published paper " on the Develop- 

 ment of some British Echinoderms," Mortensen (13), 



