554 
PKOFESSOK ALLMAN ON THE STEUCTUKE 
I have never succeeded in tracing a direct continuity of the caudal processes of the cells 
with the fibrillee of the muscular lamella. There is no doubt that the stalks of the 
claviform tissue pass into the muscular layer and become intimately associated with it ; 
but I do not believe that any more direct continuity with the individual fibrillee can be 
here demonstrated. 
KleinenberGt has further described the bodies of the caudate cells in Hydra as united 
laterally with one another, and forming the outer surface of the body, while the spaces 
which must necessarily lie between their caudal prolongations are occupied by a tissue 
composed of small non-caudate cells, to which he gives the name of “ interstitial 
tissue,” and in which he maintains that the thread-cells and the generative elements are 
formed. 
I can find nothing like this interstitial tissue in Myriothela ; and I believe that its 
place is here taken by an undifferentiated protoplasm, through which the prolongations 
of the caudate cell-clusters make their way to the muscular layer. 
If we except the case of the long transitory arms of the actinula or free locomotive 
stage, which will be afterwards described, the claviform tissue does not in Myriothela 
come to the surface of the body. Throughout the whole of the body of the adult it 
forms a deep zone, intervening between the hyaline lamella and the superficial layer of 
the ectoderm, and very distinct in sections made from specimens hardened in chromic 
acid. 
The hyaline lamella (fig. 2, i) forms the internal boundary of the ectoderm, and is 
found everywhere between the endoderm and the cellular ectoderm. It consists of 
two layers, — internally (fig. 6, c ) a perfectly transparent, thin, structureless membrane, 
and externally ( b ) a layer of fibrillee, which adheres closely to the structureless 
membrane. 
Special attention was first called to the presence of the structureless membrane 
in other hydroids by Reichert*, who named it “ Stutzlamelle ; ” but he refused to admit 
the existence of a true fibrillated layer. The fibrillated layer, however, is extremely 
distinct in almost all hydroids. In Myriothela it can be separated, after a short macera- 
tion in water, from the underlying structureless membrane. It is here composed of lon- 
gitudinal fibrillee, which adhere to one another by their sides in a stratum of a single 
fibre in thickness, which forms a continuous lamella, even after detachment from the 
supporting structureless membrane. The fibrillee are about x 2i q 0 0 of an inch in diameter, 
soft, and compressible, very transparent, with a very minutely granular structure, but 
otherwise apparently homogeneous. They show a convex surface when seen in profile 
on the folded edge of the lamella. That they are contractile elements, forming by their 
union a muscular lamella, there would seem to be little reason to doubt. They do 
not, however, possess the character of true muscle-cells. So far as I was able to 
trace them, they retain a uniform diameter, and show no appearance of nuclei. 
As already said, I have failed to find any direct continuity between the fibrillee and 
* Ueber die contractile Substanz &c. Berlin, 1867. 
