70 THE VOYAGE OF H.M.S. CHALLENGER. 
similar in appearance to the endoderm cells which line the ccenosarcal canals; and 
apparently the endodermal lining cells of the canals, from which the mass springs, are 
continuous with those composing its substance. All over the surface of this central 
mass of cells, which is invested with a thin layer of ectoderm, small globose sacs arise 
as buds, and gradually increase in size until they assume the form of the ovoid 
masses, which, being thickly set over the surface of the central mass, and hiding it 
from view, give to the active generative mass the lobulated appearance figured in 
Plate VIII. fig. 1, G. 
The young lobules when first formed appear as small rounded sacs with a thin wall 
of ectoderm, and containing a very few cells apparently derived from the main central 
mass. These cells become multiplied in number as the sac increases in size with 
progressive development. The sac as it enlarges becomes gradually pedicellate, and 
when mature is attached to the central mass by a narrow pedicle of some length. 
The walls of the pedicle are continuous with the ectodermal wall of the sac, which 
wall contains well-defined nuclei in its substance. Within the sac of the lobule a 
second sac, composed of a finer membrane, encloses the mature or developing generative 
elements. The wall of this inner sac is not prolonged into the cayity of the pedicle, 
but passing across its commencement shuts off the main cavity of the lobule from 
this latter. 
The cells contained within the young lobule maintain a closely similar appearance 
to ordinary pigment endoderm cells, until they have become multiplied into a large 
mass. On further increase they change their structure and appear as spherical, perfectly 
transparent masses, each’ of which contains a large uucleus which becomes most 
intensely stained when treated with carmine. These transparent nucleated cells, 
which are closely similar in appearance to those figured by Allman from the male 
gonophores of Laomedea flexuosa,‘ multiply further by division, becoming very minute, 
but retaining the same structure (PI. X. fig. 10, C). 
From each of these minute cells a spermatozoon is developed. The head of the 
spermatozoon appears to be developed out of the nucleus of the cell, which, as the 
process proceeds, becomes first attached to the wall of the cell on one side, and is then 
gradually drawn out in the form of a curved elongate mass along the wall of the cell 
until it assumes the form of the head of the spermatozoon, being curled round within 
the cell nearly into a circle. The various stages in development are shown on 
Plate X. fig. 11. 
The mature spermatozoa were not observed in the fresh condition. Their appear- 
ance as seen in specimens hardened in alcohol is shown on Plate X. fig. 11, g. They 
form closely felted masses within the ripe lobules, which masses do not entirely fill 
the cavities of the inner saes of the lobules. 
* Allman, Gymnoblastic or Tubularian Hydroids, Ray Soc., 1871, part 1, p. 65, fig, 316. 
