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the stomach and the posterior epidermis ; the two divisions of the alimentary canal lying in a 

 common peritoneal investment, formed exactly as in fig. 1 70. The same section shews one of 

 the ovaries (ov.) as a minute body continuous with the coelomic epitheHum, from which it has 

 probably been developed, in accordance with Masterman's statement (98, 2, p. 519) to that effect. 

 Figs. 173, 174 are drawn to shew the great proportionate size of the notochord [ncJi.) 

 in the bud, a fact already commented on by M'Intosh (87, p. 28), and the obliqiiity of the 

 first and second body-cavities to the long axis of the bud. The proboscis with its body-cavity, 

 and the pericardium have ah'eady acquired their adult relations. This bud still possesses a 

 .single pair of arms. 



My observations on the first development of the alimentary canal in the bud are, so 

 far as they go, in favour of Masterman's view (98, 2, p. 515) that the entire alimentary canal 

 develops as an ectodermic invagination ; and they are consequently opposed to those of Fowler 

 (on Rhabdopleura), according to which part of it is a derivative of an endodermic tube in the 

 stalk. From the earliest stage in which I can recognise the alimentary canal, this organ appears 

 to open definitely to the exterior by the mouth, and I have noticed no discontinuity of the 

 kind which would be implied by Fowler's view that while most of the canal is endodermic, 

 the anterior part is developed as a stomodaeum. 



With regard to the later development of the alimentary canal I cannot, however, agree 

 with Masterman, according to whom the intestinal limb of the alimentary canal is developed 

 as a diverticulum from the ventral and posterior end of the enteric sac. This is said to grow 

 in a dorsal direction towards the position of the future anus, and in Masterman's fig. 39 

 (PI. III) it is represented as traversing the coelom, and being covered throughout by peritoneum. 

 In the "transverse" sections shewing the stomach and intestine given in the same paper 

 (figs. 54 — 56) these parts are in close contact with one another and appear to be suspended 

 in a common peritoneal sac, formed by the inner walls of the two third body-cavities ; and 

 except in fig. 55 there is no indication that the peritoneum extends between them. If Masterman's 

 account is correct, it must therefore be supposed that the intestinal limb of the alimentary 

 canal, after passing along the mesentery at a certain distance from the stomach, comes into 

 contact with the posterior wall of the stomach as it travels towards the dorsal border ot that 

 organ. This, as a matter of fact, is precisely the arrangement which is found in the adults of 

 all the species, and I was accordingly prepared to find that Masterman's account of the 

 formation of the intestinal flexure was correct. But the evidence seems to be opposed to 

 Masterman's statements. The intestinal limb, at its first origin, is enclosed in a peritoneal 

 sac common to it and the stomach (figs. 170, 171 ; 56), and it becomes separated from the 

 other limb of the alimentary canal only when it has passed the stomach and has become the 

 rectum. In this position the intestinal limb has a peritoneal investment of its own, even in 

 comparatively young buds ; but I can find no evidence in the young stages of any tracé of body- 

 cavity in the concavity of the bend of the alimentary canal, as represented in Masterman's 

 fig. 39. The arrangement found in the adult must therefore be acquired at a later stage in 

 the budding, and I imagine that what takes place is that the splanchnic epithelium of the 



