90 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



the posterior enterocodes becoming horseshoe-shaped, the two horns of which lie under the horns 

 of the hydrocoele (figs. C and 7, he and by). 



Lying dorsal to the stomach we find a small enterocode which was not present in "B," or if 

 present, not in this position. It is tbe rudiment of the body cavity, whicli in the adult lies aboral 

 to the stomach and which has been recently appropriately termed the epigastric enterocoele (figs. 

 and 7, ee). 



As to the origin of this structure I have no direct observations to give, but certain facts have 

 led me to believe that it is formed from the right anterior enterocoele. These facts maybe summed 

 up as follows: In "B" no epigastric enterocode exists, but the two anterior enterocades (fig. 4, 

 aer and ael) be side by side anterior to the stomach and the posterior enteroco'les. In " C " (figs. 

 G and 7, ee) an epigastric pouch, equal in size to the right anterior enteroco'le of "B" is to be 

 found, but by the side of the oesophagus only the left anterior enterocode remains (figs. 6 and 7, 

 ael). 



During the six hours which intervene between " B" and "C" it seems hardly possible that a 

 complete formation of the epigastric enterocode should have taken place or that there should 

 have been' time for the complete degeneration and disappearance of the right anterior pouch; 

 sufficient time may have elapsed, however, for the migration of the right anterior enterocoele to a 

 position behind the stomach. 



Against such an interpretation as the above there is the fact that in no other case has the 

 epigastric enterocule been observed to take its origin from the right anterior pouch. It has been 

 described as arising from the right posterior enteroco'le, however, as has been referred to before, in 

 all the groups by Bury, and his observations have been corroborated by both Mc Bride and 

 Coto in the starfishes. 



Stage "D," 60 Horns Old. 

 (Figures 9-14.) 



The changes which have taken place in "C" to produce "D" are very marked. 



The cilia have disappeared, except in four transverse rings or bands, three of which extend 

 entirely around the body of the larva. The third ring, counting from the anterior end, is inter- 

 rupted by the aboral disk on the. ventral surface. 



This third ciliated ring first appears on the lateral bulges, which were described in "0," and 

 the fourth ring appears on a second pair of lateral bulges which originate behind the first pair 

 near the posterior end of the larva. 



The shape of the larva is no longer oval, but the posterior end has widened laterally and 

 become somewhat dorso ventrally compressed (fig. 0). The anterior end has not changed in shape 

 and may be thought of as forming the handle of the now club-shaped larva. 



The enlarged posterior end of the larva contains all its organs and is the part which will enter 

 directly into the formation of the adult ophiurid. 



From its homology with the preoral lobe and larval organ of Aster inn gibbosa I have called the 

 anterior end of the larva the larval organ. It disappears with the metamorphosis into the adult 

 form. 



The larval organ is also homologous with the stalk of the Antedon larva, although in the 

 ophiurid larva it never functions as an attachment organ. When swimming, the larval organ 

 precedes. It is filled with a network of mesenchyme cells (fig. 11, mes). 



Internally the changes have been even greater than the external ones we have just considered, 

 for it is during this period of development that the rotation and readjustment of organs takes 

 place, which is present in all echinoderms at some stage of their development. 



The hydroccele, which has begun its rotation about the (esophagus as an axis in "C," has 

 completed it in "D" and reached its definite position. 



That part of the hydrocoele whicli in "C" was situated on the left of the plane dividing the 

 larva into bilaterally symmetrical halves, now lies on the right side of the same plane and vice 

 versa. (Compare figs. and 9.) 



A revolution of 180° has taken place in the hydroccele siuce "C," to which if the 180° of 

 rotation be added, which took place up to the time of "C," we have a total rotation of 860° in the 



