and its Reproductive Cells. 37 



Lastly, Dr. Wallich, in his late interesting and indefatigable 

 study of A. villosa, thinks that the diaphane and the sarcode 

 are mutually transformable into each other, as the occasion may 

 require*. 



Now, the worst of theories is, that they take up so much time 

 in discussion before they bring out fact ; while the best of them 

 is, when multiple, that they prove that the fact is still un- 

 known. 



I shall therefore not enter further upon these speculations, 

 as the reader can best form his own opinions of them by refer- 

 ence to the papers which contain them in extenso, and will only 

 add, on this subject, that, as the diaphane is formed from the 

 sarcode, it seems to me probable that the former has a distinct 

 structure as well as office, and that, having been produced, it 

 is not reconvertible into any other organ by any process but 

 digestive assimilation. Thus, the leg of a Plcesconia has com- 

 paratively as much form and as many functions as a crab-claw ; 

 but it must not be assumed, because it is as transparent and 

 apparently as structureless as glass, that it is composed of a 

 structureless jelly-like substance which can be made to assume 

 any form and take on any function that the animal chooses, — 

 on the contrary, that it has structure and form, which the 

 microscope, Avith all its optical powers and chemical tests, can- 

 not at present define — that such structure and form is so incon- 

 ceivably delicate, and its particles held together with such 

 slight tenacity that, as a bunch of iron-filings kept in apposition 

 by a temporary magnet falls to pieces when the galvanic circle 

 is broken, so does the leg of Plcesconia undergo the same kind 

 of disintegration, viz, diffiuence, when its vitality is withdrawn — 

 and that there is no returning of this leg to the original plasma 

 with which it was formed, except by its destruction and re- 

 assimilation. I, of course, assume that the leg of Plcesconia 

 bears the same relation to Plcesconia that the pseudopod of the 

 diaphane and pellicula bears to Amoeba, viz. that it is merely a 

 modified form of the external covering — th-e one permanent, the 

 other transitory. 



Again, there is another point here, with reference to the mo- 

 tion of sarcode, which it would be well to notice, viz. the source 

 from which the rotatory motion is derived. It has already been 

 stated that this motioii stops with the cessation of the motion of 

 the diaphane, and vice versa. Is it possible that the sarcode is 

 rolled round by some peculiar undulating movement of the dia- 

 phane, after the manner that the uneven wavy surface of the 

 protoplasm in the cell of Nitella causes a rotatory movement of 

 the axial fluid ? I confess that at present I do not see anything 

 * Ann. Nat. Hist. vol. xi. p. 3/0 (1863), 



