128 ON THE DEVELOPMENT OF 
of Coryne, of peculiar pyriform vesicles, which might at first sight be 
easily taken for the reproductive sacs of the Zoophyte. They had their 
cavity in free communication with the general ccenosareal cavity of the 
Zoophyte; and an endoderm, ectoderm, and external chitinous invest- 
ment were easily demonstrable in their walls. The nature of their con- 
tents, however, at once distinguished them from the proper reproductive 
sacs of the Coryne; for in every instance they enclosed a Pycnogonidan 
(Ammothea?) The enclosed Pycnogonidan was always solitary, and in 
smaller vesicles was still embryonic; while in the larger ones, it presented 
an advanced stage of development, and was ready to escape from its con- 
finement by the rupture of the surrounding walls.” 
Now come the questions:—How is the sac formed, and how 
does the young Pycnogon get into the sac? These problems, 
are more difficult to solve than would at first appear; yet it may 
I think, be proved that at any rate the sacs are merely modified 
growths of the Zoophyte. 
If figs. 6, 7, 8,& 9, Pl. VI. are examined, it will be seen that 
the sacs present a strong likeness to “ stunted branches” of the 
polypary, as if a shoot had been suddenly brought to an abrupt 
termination by an enlargement consequent upon its occupation 
by a young Pycnogon. This view of the case becomes* more 
evident if we examine the annulated character of the sac, which 
will be found to agree closely with the same parts seen in the 
polype, which are similarly annulated. It would therefore ap- 
pear as if the young Pycnogon occupied the place of the ordinary 
polype in the Coryne. The sacs are usually found on the lower 
portions of the stems branching out from the sides, as shown in 
fig. 6, though occasionally they were met with much higher up. 
The only manner in which J can account for their position on 
the lower portions of the stems is this: the young Pycnogons, 
judging from their growth and the circumstances under which 
they are found, must have gained access to their tenements at 
an early period of the year, when the Coryne was but small; and 
the higher branches would seem to be growths, subsequent to 
the period at which larval forms abound, which have risen above 
the level of the parasitically infested shoots. 
T possess a female Phoxichilidium, taken during the present 
year, at Lerwick, by the Rev. A. M. Norman, which has several 
