AND DEVELOPMENT OE MYEIOTHELA. 
571 
to the clayiform tissue, and forms the outer surface of the body. To this layer we must 
attribute the significance of a true epidermis. It appears, however, to be absent from 
the stems of the transitory arms of the actinula after these have attained their full 
growth. In their early stages, while yet they are invaginated processes of the body 
walls, and even for some time after their complete evagination, it is present as elsewhere ; 
but during the growth of the actinula it is gradually absorbed, and then allows the 
claviform tissue to come to the surface. In the capitulum of the arm, however, it never 
disappears, being here needed as a protective envelope for the specially and more highly 
developed sensitive structures of this part. 
It is thus obvious that Myriotlielci offers no exception to the ontogenetic law, which 
derives both the central nervous system and the epidermis from the outer layer of the 
blastoderm. 
One of the most remarkable features in Myriothela consists in the presence of the 
bodies to which I have here given the name of claspers. These, as we have seen, are 
tentacle-like zooids endowed with great contractility ; and no sooner is the plasma mass, 
which is to become developed into the actinula, set free from the gonophore which had 
hitherto confined it, than one or more claspers direct themselves towards it, and fixing 
themselves to it by their sucker-like ends, hold it tenaciously during certain subsequent 
periods of its development. The manner in which the claspers thus seize upon the 
liberated plasmodium forcibly reminds us of the way in which the Fallopian tubes are 
supposed to seize the mammalian ovum at the moment of its liberation from the 
Graafian follicle. 
There is something very surprising in the selective faculty thus apparently exercised 
by the claspers ; for it is, as a rule, to the liberated plasma mass alone that they become 
attached, while no reason whatever can be assigned why they should not seize upon some 
of the neighbouring parts which are just as easily within their reach. Once or twice I 
have seen a clasper fixed to some other part of the hy droid ; but this occurrence is so 
rare that it cannot in any way be regarded as a manifestation of its normal function. 
We have at present no data which will enable us to arrive at an absolute conclusion 
as to the object gained by the seizure of the plasmodium by the claspers. It is not 
improbable, however, that it is connected with fecundation. We must remember that 
in Myriothela we have the very exceptional condition of one and the same blastostyle 
carrying both the male and the female gonophores, and, further, that the spermatozoa 
of this hydroid are remarkable for their extreme minuteness ; they are smaller, indeed, 
than in any other hydroid with which I am acquainted. Now I have never seen the 
spermatozoa escape spontaneously as in other hydroids from the gonophore; and when one 
of the Myriothela gonophores containing mature active spermatozoa is subjected to slight 
pressure, it is not through any breach of continuity in the thick external walls of the 
gonophore that the spermatozoa are ejected, but through the walls of the spadix, which 
appear to be easily ruptured. In this way they pass directly into the gastric cavity of 
the blastostyle, and through this may be easily conducted to the base of a clasper, and 
