218 BUNTING. [Vote LX. 
same vessel. He has also observed that this method of 
beginning at one pole and passing through to the opposite one, 
(“«Schneidende”’), is to be found among the metagenetic 
medusae; while the circular method is to be observed in the 
hypogenetic forms. 
In about two and one half hours a spherical mass of cells 
(Pl. II, Fig. 30) is formed, which is motionless. In ten or 
eleven hours after the first cleavage this elongates, becomes at 
first oval in shape (Fig. 31), still opaque, and having, when 
viewed by the reflected light, the same greenish tint as the 
ovum. The embryo remains unciliated and motionless, for 
about sixteen or seventeen hours, when we find the opaque 
planula gradually revolving; we see later that it becomes further 
elongated (Fig. 32) and pinkish in tint, resembling the color 
of the adult animal. When viewed by transmitted light, we 
find the embryo to have an inner mass surrounded by a slightly 
transparent zone, in which numerous nematocysts appear; 
these are collected in greater numbers at the tapering end 
where the cilia are shorter, while the forward directed blunt 
portion contains longer cilia and fewer nematocysts. In about 
thirty-six hours, the ectoderm of the broad end has much 
increased in thickness, preparatory to the formation of a disc 
to serve as a means of attachment. The planula becomes so 
attenuated and tapering, that it very much resembles a tentacle 
of the adult hydroid. 
After thirty-six to forty-eight hours, those planulae that were 
to develop further became attached at the broad end; they 
then contracted, remaining in this position for varying periods 
of time; under most favorable conditions they became hydroids 
.in about four days. From the base of the hydroids we find 
at first “stolon-like”’ outgrowths (Pl. III, Fig. 64) that later 
are to form the hydrorhiza. The tentacles first appear as 
projections from the wall of the hydroid. The mouth has 
been formed in the hydroid with four tentacles, as is shown 
by a surface view in Fig. 65, and the hydrorhiza now consists 
of. four tubular outgrowths (Z). In a six-tentacled polyp we 
see these tubes increased in length, with one turned up as 
though about to form another polyp (Fig. 66). 
