TROPIOMETRA CARINATA. 17 



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

 crelom. 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 ccelom has formed the vertical mesen- 

 tery (the details of this process could not be made out) (plate vn, figure 6), 

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

 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 vn, 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 per haps 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 vm, 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 Seeliger. 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 Pentacrinoids. 

 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 vm, figure 1) the cover- 



