266 E. W. MACBETDE. 



unlikely that they 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 (PI. XVII, fig. 109, bip. 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 perihsemal 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. 

 Cuenot 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-organs of Asterina are all developed in connection 

 with the appendages of the water-vascular system. The eye 



