136 BULLETIN OF THE 
The apex of the anal lobe is densely pigmented, and the walls are 
supported by highly ramified divisions of the anal rods (posterior and 
anterior), which interdigitate and form an intricate network. An anus 
is present, and the intestine is elongate or flask-shaped. The mouth is 
commonly widely open, circular, with ciliated lips. The cesophagus is 
densely ciliated on the interior walls. The pluteus moves from place to 
place easily but not rapidly, and is just visible to the naked eye. The 
length is .85 mm. ; diameter of the body .20 mm. 
One of the most striking differences between the adult pluteus of Echi- 
narachnius and A, Agassiz’s drawing of that of Strongylocentrotus of the 
same age, is the existence of large pigment spots near the distal end of 
each arm, while the anterior and antero-internal arms of Strongylocen- 
trotus have no such spots, at least of the great prominence which we 
find in Echinarachnius. The pluteus of Strongylocentrotus, according 
to A. Agassiz, has ciliated epaulettes. These structures are not repre- 
sented in the pluteus of Echinarachnius. Like the pluteus of Echino- 
cyamus, as figured by Miiller, Echinarachnius has no ciliated epaulettes. 
The resemblance of the pluteus of Echinarachnius to that ascribed to 
Echinocyaraus is very great. If we compare the figures given by Miiller 
and those of the Echinarachnius pluteus here figured, we notice one or 
two marked differences between them. The arms of the pluteus are 
much longer and larger in Echinarachnius than in Echinocyamus. The 
posterior and antero-lateral rods of both genera are latticed. The an- 
tero-lateral and antero-internal in both are not connected with the body 
system of rods. The anterior lobe before the origin of the antero- 
internal arms is longer in Echinocyamus than in Echinarachnius. The 
characteristic pigment spots of the ends of the arms of Echinarachnius 
are not found in Echinocyamus. The difference of the young from the 
adult sea-urchin formed from the pluteus of Echinocyamus has at- 
tracted the attention of Miiller. The young Echinarachnius raised 
from the pluteus is somewhat different from Miiller’s figures of the 
young Echinocyamus.* 
the suspensoria are mesodermic, as Selenka says. In Agalma these structures 
appear to be epiblastic. It may be said, however, that they originate from the 
epiblast, just as the mesoblastic cells themselves may originate as simple exten- 
sions and buds. The homology, therefore, of the suspensoria and the filament in 
the primitive hydrophyllium cannot be made out at present. It may be said that 
the likeness between the two is great. (For filaments in the primitive larva of 
Agalma, see Embryology of Agalma, Bull. Mus. Comp. Zodl., XI. No. 11.) 
* Jt is taken for granted that the pluteus described by Miiller is an Echinocy- 
amus, although he did not raise it in the egg. 
