222 ON THE EXISTENCE OF CELLULOSE IN ASCIDIANS 



exists in the same condition as the calcareous salts in bone, or as the 

 chondrin in cartilage. 



Substituting cellulose for calcareous salts, the structure of the test 

 of Salpa is exactly that of the bone of plagiostomous fishes (Leydig, 

 Beitrage zur Anat. d. Rochen. Haie, 1852). 



2. Pyrosonia has a firmer test, which contains far more cellulose. 

 This is more readily detected by the iodine and sulphuric acid, but in 

 its relation to a general nitrogenous basis precisely resembles that 

 of Salpa. 



The nucleated cells differ from those of Salpa in being thrown 

 into very long processes which meet and unite — ^just like those of 

 Volvox as described by Mr. Busk. On the other hand they assume 

 exactly the appearance of bone corpuscles — though the processes are 

 generally straighter and are rarely branched. 



Making the same substitution as before, we have in the test of 

 Pyrosoma a structure comparable to that of the lamina papyracea of 

 the ethmoid bone. 



3. In the Phallusm there is an indistinctly fibrillated basis, 

 containing a large amount of cellulose in all essential respects 

 resembling the foregoing. Nucleated cells, provided with irregular 

 processes, are scattered through this substance. 



The large cells described by Lowig and Kolliker and by Schacht 

 are not cells at all, but are vacuolse — very probably produced, like the 

 cancelli of ordinary bone, by interstitial absorption. There is no 

 lining membrane like that described by Schacht. With care the walls 

 may be coloured deep blue to their very edges. The appearance of 

 fibres is produced by the striation which runs through the whole mass, 

 and is especially distinct upon the walls of the cavities. It exists 

 after the action both of sulphuric acid and of caustic soda. 



Lastly, the resemblance to perfect bone is completed by the 

 canals which are hollowed out in the substance of the test for the 

 vessels (or rather prolongations of the outer tunic, which is what they 

 really are). In the walls of these canals I have frequently seen the 

 nucleated cells projecting just as Kolliker describes them in the 

 "medullary canals" or developing bone (Mikroskopische Anatomic, 

 p. 369). 



The spiral fibres described by Schacht are the muscular fibres 

 surrounding the wider portions of the vessel-like prolongations. 



Finally, with regard to the relations of the cells to the cellulose — 

 anatomically and physiologically — I do not see any force in the 

 distinction attempted to be established by Schacht between animals 

 and plants. The nucleated cell of the Ascidian tunic answers exactly 



