266 BULLETIN OF THE 
tive larva. On the right-hand side of the cavity of the primitive 
hydrophyllium is a cluster of cells of red color, which is the beginning 
of a second similar serrated hydrophyllium. This latter cluster, how- 
ever, has not raised itself any considerable amount above the surface of 
the yolk. The longest diameter of the primitive hydrophyllium in 
Fig. 14 is .75mm.; the thickness at the distal side, .17 mm. The 
length of the primitive cavity is .25 mm. ; its breadth is.10mm. The 
float is almost .10 mm. in diameter. It will be seen from these meas- 
urements that the scale has now reached a very great size as compared 
with its dimensions in earlier larve. It has now the maximum size 
to which it ever attains. 
Fate of the Primitive Hydrophyllium. 
It is known that this primitive hydrophyllium is a temporary or 
embryonic structure; but its fate, whether it is simply thrown off or 
absorbed, is not at present definitely made out. Both Heckel and 
Metschnikoff have pointed out that it is a provisional structure, but 
neither has traced it far enough in the last phases of its history to sat- 
isfactorily show whether it is simply discarded, absorbed, or passes with 
external changes of outline into some other structure. The most defi- 
nite statement which we have is as follows. Metschnikoff says, “das 
erstgebildete kappenformige Deckstiick abgeworfen wird” in the genus 
Agalma. 
The primitive hydrophyllium of Agalma elegans suffers many modifi- 
cations in external form in some of the older stages ; but whether these 
modifications were abnormal, resulting from the fact that the animal is 
in confinement, was not determined. It seems to me more natural to 
suppose, that, instead of being thrown off in the subsequent stages, the 
primitive covering-scale passes by a few modifications in its external 
contour into some other organ, probably a differently formed covering- 
scale. 
Fig. 15 represents the larva of Agalma on August 10, four days after 
the capture of the parent. This larva was picked out of the water, 
in which it was freely swimming below the surface. The figure repre- 
sents the larva as seen from that pole which is opposite the germina- 
tive pole, so that the various organs which have appeared near that 
region are seen through the yolk contents. This position, assumed 
while the egg is floating, is that which is best adapted to exhibit the 
