4 PllOPESSOR ALLMAM. 



may sometimes be detached from the muscle processes. It 

 is during life very soft, clear and colourless, and destitute of 

 granules. It is not coloured by iodine or carmine, but under 

 the action of gold chloride it acquires a straw colour. It 

 is to the membrane thus formed by the muscular fibrilloe and 

 their connective medium that Reichert has given the name 

 of "Stiitzlaraelle." 

 eJ^^ j From the peculiar fol'm of the large emJbdermal cells there 

 necessarily lies between their outer ends, where they are in 

 close contact with one another, and the muscular lamina, 

 which lies in contact Avith the endoderm, a system of inter- 

 communicating lacunae. These lacunse are filled by the 

 smaller cells already mentioned. The tissue thus formed by 

 the small cells he names the interstitial tissue of the 

 ectoderm; it necessarily forms a network and not a con- 

 tinuous layer. The cells composing it are fusiform or 

 flattened, and their protoplasm surrounds a relatively large 

 nuclevis which often forms the chief mass of the cell. 



It is in the cells of this interstitial tissue that the thread- 

 cells are formed. These bodies are described as commencing 

 in the form of a sphei'ical clear space which shows itself 

 by the side of the nucleus, and which, without being sharply 

 circumscribed at first, gradually acquires a double contour, 

 and assumes the definitive form of the thread-cell within 

 which the spirally wound filament is developed. It would 

 seem that some time after the completion of the thread-cell 

 the nucleus of the generating cell regularly disappears. This 

 cell then loses its granular contents and surrounds the thread- 

 cell as a spherical or oval covering. The thread-cells are 

 now pushed forward from the deeper parts where they 

 originate towards the surface, where they lie between the 

 large cells or become even imbedded in their protoplasm. 

 Kleinenberg is unable to add any fact to what is already 

 known regarding the structure of the mature thread-cell. 



The structure of the foot differs from that of the rest of 

 the body in the fact that the interstitial tissue, and con- 

 sequently the thread-cells which originate in this tissue, are 

 entirely absent from it. 



Kleinenberg's speculations as to the physiological signi- 

 ficance of the large ectodermal cells and their fibre-like 

 processes are full of interest. These processes alone 

 possess contractility, the cell-bodies belonging to them being 

 entirely passive during the motions of the animal. He 

 does not think that we can compare morphologically 

 the tissue thus formed to the known tissues of any other 

 animals, or that we can recognise in it physiologically 



