TROPIOMETRA CARINATA. 17 



of the entoderm, and they are now distinguished as the oral and aboral 

 coclom. Their shape and extent is shown in plate vi, figures 1 to 4 and 7 to 9; 

 plate VII, figures 6 and 7. The aboral coelom has formed the vertical mesen- 

 tery (the details of this process could not be made out) (plate vii, figure G), 

 and in it the axial organ has made its appearance (plate vi, figure 7; plate vii, 

 figure 8) . Also the chambered organ is assuming its final shape and is seen 

 very distinctly continuing through the whole length of the stalk (plate vi, 

 figure 7, plate vii, figures 4 and 5) ; but this is already the case previous to 

 fixation, as seen from plate vi, figures 2, 3, and 5. 



The entoderm undergoes very important changes. First the rectum 

 develops after the fixation (plate vi, figure 7), but it does not open outwards; 

 there is not even an invagination of the epidermis to meet it. Then the mouth 

 opens into the vestibulum. There is an invagination of the thick ectodermal 

 layer forming the bottom of the vestibulum, which meets the entoderm and 

 forms the esophagus. Plate vii, figures 8, 3, and 7, show the different stages 

 of this process. 



A very conspicuous feature in the development of the intestinal tract in 



Antedon is the wandering of cells from the wall of the stomach into its lumen 



to be devoured there and thus to constitute nourishment for the young 



Crinoid until its mouth opens and it can procure its own food (Seeliger, 



pp. 287-291). This very remarkable way of feeding itself is not seen very 



plainly in Tropiometra; in fact, I am not at all sure that it does occur there. 



It is true that in the specimen from which plate vii, figure 3, is made there 



is a mass of the fine grains to be seen in the stomach, which might perhaps be 



such cells about to be digested ; but in other specimens I have failed to find 



anything of the sort — for instance, in plate vii, figure 4, the stomach shows 



itself as empty as possible; also, these grains which are supposed to represent 



the residue of cells being dissolved and digested are found not only in the 



stomach but also in the stalk (on the right side in plate vii, figure 3). In the 



specimen figured in plate viii, figures 1 to 3, similar grains are seen in the 



covering of the vestibulum, but not in the stomach. These facts do not 



speak in favor of regarding this as a proof that the young Tropiometra obtains 



its food in the same remarkable way as in Antedon. Upon the whole, the 



object of these cells is, certainly, not to be devoured by the larva, as assumed 



by SeeUger. I think Bury {op. cit., p. 273, etc.) is right in regarding them 



as phagocytes, which produce an histolysis of the larval tissues, especially 



the entoderm. 



5. THE PENTACRINOID STAGE. 



(Plate VIII.) 



As mentioned in the introduction, some of the larvae attached themselves 

 to the surface film of the water^ developing into very fine Pcntacrinoids. 

 The specimens used for section are from that lot. None of them reached so 

 far as to open up the vestibulum, but (as seen in plate viii, figure 1) the cover- 



