260 BULLETIN OF THE 



as the axis of the adult Agahna, although it is not clear that the right 

 and left sides of the disk-like elevation correspond with the right and 

 left sides of the appendages later found on the adult Agalma axis. The 

 general appearance of the yolk and the size of the egg is approximately 

 the same as in the preceding stages. The right and left sides used for 

 figures up to PI. III. fig. 4 have not the same significance as here 

 interpreted. 



The next oldest larva (fig. 9) differs primarily from the last in the 

 greater elevation and prominence of the layers formed on the yolk. The 

 epiblast and hypoblast are much thicker ; the former has a reddish, 

 the latter a yellowish color. The constriction around the elevated 

 disk between its edges and the surface of the ovum has deepened o. 

 the distal side of the elevation as seen in profile, but the indentation 

 is very slight on the proximal side. 



Within the disk a gelatinous layer, so transpai-ent as to be invisible, 

 has formed by a separation of the epiblast and hypoblast. The thickness 

 of this layer is greatest near the distal end of the disk. Yellow and 

 reddish pigment is found in the epiblast on the surface of the yolk sac. 

 It was also noticed that the epiblast at 2^^^- ^I/-, ^^ear the proximal end of 

 the elevated disk, is much thicker than that near the distal side, and 

 that there was a tendency to form a slight epiblastic elevation at that 

 point. If the reader will compare the figure of this stage with one of 

 about the same age by Metschuikoff, he will find a great difference in 

 external shape between the two. My larva is approximately the same 

 as PI. VIII. fig. 5 in the oft-quoted work by that author, who says that 

 his larva is five days old. My adult Agalma was put in the aquaria 

 on August 6, and the stage represented in fig. 8 was found free in 

 the water on August 8, or two days later. I likewise picked out of the 

 same water three days after, or five days after the adults were put there, 

 larvsc of the same age, while with these were still others much farther 

 advanced, and some which were just passing through the early stages of 

 segmentation of the egg. 



I find a discrepancy, which may be a generic difference, in the rate of 

 growth day by day recorded in Haeckel's observations on the develop- 

 ment of Crystallodes, and MetschnikofF's of Agalma. In larvee of Crys- 

 tallodes four days old the float was as f;ir advanced as in the Agahna six 

 days old of Metschuikoflf, while on the second day both the Agalma and 

 Crystallodes larvce were still in a morula stage. These discrepancies 

 arise from the difference in the mode of growth of the float in the genera, 

 or from the fact that different clusters of eggs, or different members 



