MUSEUM OF COMPARATIVE ZOOLOGY. 15 
anterior lobe, passing to the anterior arms. The four arms which arise 
from the anterior lobe are called the anterior, a7, and the antero-inter- 
nal, air. Both are furnished with a solid non-latticed central axis or 
calcareous rod. The anterior rods are fastened to the general cal- 
careous framework of the body; the antero-internal are free, united to 
the former by muscular attachments. The larva may be compared to 
the parts of a chair, the antero-internal rods forming the front legs, the 
anterior the hind legs, and the oral lobe the back by which these rods 
are joined to the body of the pluteus. The distal ends of the anterior 
rods are more widely separated than the antero-internal. The anterior 
rods are skirted by a ciliated band continued from the antero-lateral as 
mentioned above. They bear a red pigment spot at a short distance : 
from their distal end. 
The last pair of arms to be mentioned, the antero-internal arms, ar, 
are joined together at one end by the ciliated band which passes upon 
their rim from the anterior arms, and is joined between them, just as 
the other end of the circuit is joined on the medial line between the 
posterior rods. One edge of the junction of the two antero-internal 
arms forms one of the so-called lips of the mouth, Pl. VII. fig. 2. The 
oral opening, or, is placed between this structure, and the ciliated band 
joining the two posterior rods or arms. The two antero-internal arms 
commonly want the prominent pigmentation of the distal ends of the 
other arms. In one or two specimens, however, pigmentation was ob- 
served on the distal end of the antero-internal arms. As the calcareous 
rods which support the antero-internal rods have a separate origin from 
the rods of the body system, they are capable of movement, and are not 
fused with the other rods. A number of muscular threads by which 
this movement is brought about can be seen in the inner angles formed 
by the rod and the neighboring anterior rods, Pl. VII. fig. 18. In the 
interior of the body we find that the larger part of the body of the plu- 
teus is occupied by the stomach. Between the stomach and the epi- 
blastic layer which covers the body of the pluteus many cells are found, 
some of which are yellow in color. Filaments or threads connect the 
hypoblastic wall of the stomach and superficial epiblast.* 
* While studying the Embryology of Agalma similar threads were noticed 
passing from the epiblast of the primitive hydrophyllium to the hypoblastic lining 
of the same. Similar threads are known in many worm larve. If these struc- 
tures are the same as the so-called suspensoria (Selenka) of the gastrula, we may 
reasonably doubt whether Selenka is right in supposing them derived from the 
mesoderm cells. As far as observation has gone there is no reason to doubt that 
