572 
PROFESSOR ALLMAN ON THE STRUCTURE 
thence carried through its narrow axial channel to its summit, where this has become 
attached to the plasmodium just liberated from the female gonophore. When once 
arrived there the spermatozoa may make their way through the terminal tissue of the 
clasper, and be thus brought into immediate relation with the plasmodium, whose 
investing membrane is at this time exceedingly thin and weak, a process which will be 
obviously facilitated by the exceptional minuteness of the spermatozoa. 
We should further bear in mind that it is not until after the seizure of the plasmodium 
by the claspers that we have any evidence of the phenomenon of segmentation — a fact 
which renders it highly probable that the act of fecundation also takes place subsequently 
to the seizure. Spermatozoa, if searched for in the cavity of the clasper, would probably 
be found there ; but, short of their detection in this situation, we have a combination of 
facts about as strong as could be desired, all tending to the conclusion that the function 
of the claspers is that here suggested, and offering a case in many respects parallel with 
that of the hectocotyle in the Cephalopoda, or with certain phenomena of fertilization 
among the Algse. 
Explanation of the Plates. 
PLATE 55. 
Fig. 1. MyriotJielci phrygia. A group, natural size, attached to a stone; some of the 
individuals contracted, others extended. 
Fig. 2. Magnified view of an individual extended. 
a, a , a, a. Blastostyles ; b , b, b, b. Gonophores ; c, c, c, c. Claspers ; d. Basal 
portion of the hydranth invested with its perisarc ; e, e. Processes of attach- 
ment. 
Fig. 3. Magnified view of an individual contracted. 
PLATE 56. 
Fig. 1. Transverse section of the hydranth at some distance behind the mouth. Mag- 
nified. 
a. Endoderm ; b. Villi-like processes of endoderm projecting into gastric 
cavity ; c. Ectoderm ; d, d, d. Tentacles. 
Fig. 2. Portion of transverse section of hydranth, still more magnified. 
a. Endoderm ; b. Villi-like processes from the free surface of endoderm ; 
c, c. Small spherical cells loaded with coloured ' granules, and terminating 
the villi ; d. Thin stratum of homogeneous protoplasm extending over the 
free surface of the endoderm ; e, e. e. Pseudopodial processes emitted from 
the protoplasmic stratum, along with which fine vibratile cilia are also seen 
extending into the gastric cavity ; f. Base of a tentacle ; g. External layer of 
cellular ectoderm; h. Internal layer of same (clavate tissue); i. Hyaline 
lamella. 
