384 E. W. MACBRIDE. 
unlikely that their muscles are of peritoneal origin, and their 
position in other Asterids where, as in Asterias, for example, 
they occur on the skin covering the spines, growing even from 
their tips, makes such a supposition almost impossible. There- 
fore we must postulate some muscles of mesenchymatous origin 
for Asterina, although all those which I have examined are of 
epithelial origin. 
The development of the nervous system has advanced greatly, 
and has reached, as soon as the metamorphosis is complete, 
its final form ; this is shown in fig. 141, taken from the same 
specimen as fig. 146. The ectoderm cells have increased 
immensely in number, and become excessively filamentous, so 
that the nuclei are many layers deep; the fibrillar layer has 
increased very much in thickness. It is traversed by vertical 
fibres which sometimes branch and sometimes have small 
nuclei on them; these are in continuity with the ectoderm 
cells, but are probably of non-nervous character. Sections 
parallel to the disc show that numerous little bipolar cells are 
embedded in the mass of fibrils (Pl. 24, fig. 109, dip. gang.). 
Since these cells are not present in the just metamorphosed 
form, they must be ectoderm cells which have passed in, and 
occasionally one sees a cell just at the boundary of the fibres 
apparently in the act of passing in. The perihzemal spaces 
become closely apposed to the nerve-cord, no mesenchyme 
being left between (ph. fig. 141) ; the vertical fibres do not, how- 
ever, arise in connection with the epithelium of these cavities, 
since they are present before this close apposition takes place. 
Cuénot states that all the ectoderm cells of the nerve-cord end 
in the vertical supporting fibres described above. This is a 
bold statement which it is quite impossible to prove by sections, 
and which is most improbable. As a matter of fact these 
vertical fibres are not present in nearly large enough number 
to account for all the ectoderm cells ; and Hamann’s statement 
(8) is probably correct, that many of these end in fine processes 
which lose themselves in the mass of fibrils. 
The sense-orgaus of Asterina are all developed in connection 
with the appendages of the water-vascular system. The eye 
