558 
PROFESSOR ALLMAN ON THE STRUCTURE 
lamella ( b ) is very well developed, and is succeeded externally by a zone of claviform 
tissue ( c ) overlaid by a zone composed of small round cells with nearly colourless 
granular contents, and lying two or three in depth ( d ). Among these the oviform and 
fusiform thread-cells are scattered in considerable abundance. 
The terminal enlargement (e) of the clasper differs from its narrower portion chiefly in 
the great development of the claviform tissue which constitutes the principal mass of 
its substance. The caudal prolongations of the cells (fig. 12) composing this tissue are very 
long, and do not unite with one another, so as to constitute botryliform groups to 
the same extent as in the corresponding tissue in the ectoderm of other parts of the 
hydroid ; they radiate from the hyaline lamella, and possess a considerable resemblance 
to the constituent elements of the rod-like tissue in the tentacles. On the summit of 
the clasper, where this organ exercises a special function of adhesion, the thread-cells so 
well developed in other parts of the ectoderm are deficient. 
The function of the claspers, as we shall see more particularly under the head of 
development, is that of seizing, on its escape from the gonophore, the plasma mass 
which is to become developed into an embryo. 
The gonophores (Plate 55. fig. 2, b, b , b, and Plate 57. fig. 14, c, c, d ) show nothing like 
a medusal conformation. They are simple sporosacs of a spherical form, supported on 
very short peduncles, which spring without any definite arrangement from the sides of 
the blastostyles. They show no definite order of arriving at maturity, the more mature 
gonophores being sometimes at the distal side of the younger ones, sometimes at their 
proximal side, and sometimes scattered among them. Their law of maturation is thus 
strikingly different from that of the gonophores of most other hydroids, in which we find 
either a constant centripetal or a constant centrifugal order in the periods of their first 
appearance and of their arrival at maturity. 
Myriotliela is also extremely exceptional in carrying on the same hydranth, and even 
on the same blastostyle, both male and female gonophores. So far, however, as my 
observations extend, the male gonophores are borne at the distal side of the female 
ones. No external difference between the two can be detected beyond thefa,ct that the 
mature males are much smaller than the mature females. 
In the walls of the mature gonophores (Plate 57. figs. 7, 10, 12), whether male or 
female, several distinct structures may be demonstrated. Most externally is a zone of 
spherical cells (fig. 12, a), which for the most part contain clear colourless granules; but 
towards the summit of the gonophore some of these cells are filled with purplish 
pigment granules, and form a coloured circle surrounding the distal pole of the gono- 
phore (fig. 14, c, c, d). Passing from without inwards, this is followed by a zone of 
clavate tissue (fig. 12, b), and this by the structureless lamella ( c ) overlaid by muscular 
fibrilke. These three zones are direct continuations of the corresponding elements in 
the ectoderm of the blastostyle. 
Lying immediately within the hyaline lamella is another cellular layer (fig. 12, d). 
In its thickness this layer corresponds to the depth of a single cell. Most of the cells 
