no Papers from the Marine Biological Laboratory at Tortugas. 



plate, it is a remarkable fact that at the tip of the arm there are no tentacle- 

 scales at all. It is not until a dozen or more segments are formed that the 

 first tentacle-scale appears and it is associated with the side arm-plate, 

 arising near its outer margin, at the base, from a separate center of calci- 

 fication. The origin and appearance suggest homology with the arm- 

 spines. Almost immediately after the formation of the first tentacle-scale, 

 a second one associated with the under arm-plate begins to form and is 

 usually visible after one or two segments have given rise to the first one. 

 The exact place of appearance of the tentacle-scales is subject to a good 

 deal of individual variation; thus in a specimen with 21 or 22 segments in 

 each arm, the terminal 15 or 16 have no tentacle-scales, but the sixteenth or 

 seventeenth has one associated with the base of the side arm-plate, while 

 the second scale may be seen on the eighteenth or nineteenth segment in 

 4 arms, but not until the twentieth in the fifth; on the other hand, in older 

 specimens, with 30 or 40 arm-joints, the first tentacle-scale may appear only 

 12 segments from the tip of the arm and the second on the fourteenth. The 

 first tentacle-scale has every appearance of being the homologue of an 

 arm-spine, but the second is apparently quite a different organ. It must 

 be considered as a possibility that this second tentacle-scale in Amphipholis 

 is homologous with the single tentacle-scale of Ophiactis, but the question 

 involves the examination and study of many related genera before it can be 

 answered. 



SUMMARY OF GROWTH CHANGES IN AMPHIPHOLIS SQUAMATA. 



1. The disk-covering when the adult form is first assumed consists of the 



typical primary plates, figured by Fewkes and by Ludwig. Rapid 

 growth, however, soon decreases the conspicuousness of these 

 plates and in the adult they are seldom recognizable. 



2. The torus of the adult bears 4 teeth, which do not arise as outgrowths 



from it, but originate from separate centers of calcification. The 

 uppermost tooth is oldest, the lowest youngest. 



3. The second adambulacral plate, which becomes the adoral plate in 



the adult, does not bear a spine at its distal end at any stage of 

 its development, nor does a spine arise at any time by a separation 

 of a projection of the original plate. 



4. The oral papillae arise from separate centers of calcification associated 



with the first two adambulacral plates. They may be homologous 

 with tentacle-scales. 



5. At an early stage of development, Amphipholis has only 2 oral papillae 



on each side of the jaw, as in Amphiura. It may therefore be 

 said to pass through an Amphiura stage. 



6. The vertebrae of Amphipholis are essentially like those of Ophiactis, but 



have retained certain youthful features, greater relative length, 

 less relative height, narrower protapophysis, more conspicuous 

 parapophyses, and less well-marked epapophyses. 



7. Arm-plates arise in the same sequence as in Ophiactis, but the side 



arm-plates of any one segment are never separated from each other, 

 either above or below. The arm is thus more youthful than that 

 of Ophiactis. 



