118 BULLETIN OF THE 
opment of Ophiothrix, “Ces deux masses cellulaires ne sont pas, comme 
Ya supposé M. Balfour, dues a des diverticulum de l’archentéron, sem- 
blables aux cavités vaso-péritonéales des Holothurins, mais elles sont 
des produits d’une formation directe, comme cela a lieu pour l’estomac.” 
Pl. I. fig. 18, shows a larva slightly older than the gastrula last 
described. If we look at this larva from the flat or ventral side, we 
notice on each side of a single opening * small pigmented protuberances. 
These prominences in the future growth of the larva become more and 
more extended, and even in their earliest form give evidence that they 
develop into the lateral arms of the pluteus. The larva is now three 
days old, and has begun to assume a form like the youngest Ophiuran 
pluteus described by others. The longitudinal axis is.18 mm. ; the dis- 
tance from the tip of one lateral prominence to the opposite is .16 mm. 
The anal lobe has grown more pointed than in the larva just described, 
the body of which is about spherical. The oral lobe is smaller than the 
anal, although similar to it in form. It isas yet undivided. A mouth 
leading into a cavity opens on the upper pole on the ventral side of the 
oral lobe, and a broad band of cilia extending along the lateral arms 
surround the mouth, the oral lobe, and the ventral region of the body. 
The opening thus surrounded by a ciliated band is easily seen. Its lips 
are richly ciliated. 
The limestone rods have already been formed in the body, Pl. IL 
fig. 19. There are two centres of formation of these bodies ; but these 
centres of calcification are at first not joined. The limestone rods, sp, 
originate as spicules with three prongs. One prong extends into the 
lateral rod, another in the direction of the anal lobe, and a third into 
the oral lobe. Later, a fourth process is formed from the common 
union of the three already mentioned, which extends to the middle line 
of the dorsal side. 
The amceboid or mesoblastic cells are formed throughout the region 
of the larva, between the epiblast and hypoblast. They are spherical, 
sometimes branched, forming suspensoria connecting the wall of the 
* Still further observation is necessary to show whether the mouth of the gas- 
trula of Ophiurans becomes the mouth of the pluteus, or whether, as in Holothu- 
rians (Cucumaria,) Selenka, the Starfishes (Asterius vulgaris,) A. Agassiz, (Aster- 
ina,) Ludwig, and in some Echinoids (Strongylocentrotus) according to Krohn and 
A. Agassiz, the gastrula mouth becomes a vent. I have not observed an anus in the 
pluteus of Ophiopholis. The single opening is, therefore, supposed to be the gas- 
trula mouth. Whether, as in some other Echinoderms, a new opening is formed, 
and the gastrula mouth becomes an anus or not in later stages, was not observed. 
