72 



ANDREWS. 



mic and wave-like alternation. This sequence of actions is 

 common in cilia not only when first formed but after any rest- 

 ing period later. It is also possible that they are at first covered 

 and bound together by a delicate film of protoplasm so as to 

 form a striated undulating membrane, but even then they are 

 already formed organs and filose products. 



[80] The length of cilia was found in all cases to exceed 

 that given them in published drawings. From the Protozoa to 

 the Rotatoria, and from these to starfish and sea-urchin larvae, 

 rays, cilia, sense-hairs, and flagellate appendages seem to be 

 longer than is figured, except in Messrs. Drysdale and Dal- 

 linger's researches upon the monads. This was evident to me 

 years ago with no powers higher than a J^ Crouch objective, 

 but then it was supposed to be economy of space which had 

 led to suppression of the total length. I am now inclined to 

 think that these processes are not seen to their full extension 

 by most observers, and there has been evidence in many cases 

 that the finest extensions eluded my most carefully arranged 

 optical conditions. 



[8 1 ] Pellicles spin almost everywhere ; and under very adverse 

 physical conditions, as one would think. The interalveolar 

 substance seems to be irrepressible. What more unlikely 

 physical opportunity for such activity than from the inside of 

 alveoli of Biitschli's structure } Yet this I have many times 

 seen, even during strongly contracted states of an area, which 

 meant great compression of the alveoli. And in coarser alveoli 

 of fluid endosarc such extensions are not uncommon. 



[82] The interalveolar stuff spins itself out also along paths 

 within itself ; that is, protoplasmic processes, like delicate 

 heliozoan rays, are extended through the interalveolar foam, 

 between the vesicles, just as such rays are often forced through 

 gelatinous material of some considerable density surrounding a 

 radiolarian. Indeed, the protoplasmic substance is found acting 

 and reacting on and to itself, as if it were a true fluid environ- 

 ment. In this fact I find one of the strongest arguments yet 

 given for accepting the vesicular nature of the substance. 



[83] Cilia, fibres, and undulatory membranes are formed by 

 interalveolar substance in the heart of unbroken networks of 



