TEGUMENTARY ORGANS 40S 



Kolliker was unable to find any cellular structure in the columns 

 or laminae themselves, but describes a layer of nucleated cells under 

 the shell, which he regards as the agents in its secretion. Some 

 researches recently made by H. Miiller (Gegenbaur, Kolliker and H. 

 Miiller, /. c.) corroborate this view. He finds the shell of the Loligidae 

 invested by an excessively vascular membrane, which is almost 

 wholly covered by a layer of epithelial cells towards the shell. On 

 the dorsal surface they are for the most part rounded ; on the 

 abdominal surface, and particularly towards the anterior point, they 

 form narrow cylinders which attain a length of as much as O'Oj'". 

 They appear to give rise to the structureless layers of the shell. The 

 lateral styles of the Octopods present similar relations. 



The structure thus described, though apparently so widely 

 different from that of ordinary molluscs, does not really differ very 

 widely from the cancellated shell structure of Rudistes, &c., or still 

 better of Pleurorhynchus as described by Dr. Carpenter. If we leave 

 out the sides of the hollow prisms in the latter shell in fact, it will 

 correspond exactly with one lamella of the ventral layer of the 

 sepiostaire. 



For a comparison of the shells of Spirula and Belemnites with 

 those of Sepia and of Gasteropods, I must refer to Dr. Carpenter's 

 Memoir so often cited. 



2. Conversionary integument of the Molliisca containing celhdose. — 

 This form of integument has hitherto been found in the Ascidians 

 alone, in which the existence of cellulose was first detected by 

 Schmidt in 1845. Schmidt's discovery was confirmed, the fact of the 

 existence of cellulose in all the genera of Ascidians determined, and 

 the chief morphological characters of their test set forth in the 

 memoirs by Lowig and Kolliker " Sur les Enveloppes des Tuniciers," 

 which appeared in 1846, since when further investigations have been 

 made by Schacht and by myself I must refer the reader to these 

 papers for an account of the various opinions which have been enter- 

 tained with regard to the structure of the Ascidian test, as I can only 

 lay before him what are in my belief the facts of the case. 



The test of the Ascidians is never composed of pure cellulose, but 

 consists of an animal membranous matrix, to which the cellulose has 

 the same relation as the calcareous salts have to the membranous 

 basis of bone or of shell. The cellulose is, in fact, diffused through 

 the membranous matrix, thoroughly impregnating it. 



This membranous nitrogenous matrix in which the cellulose is 

 deposited, presents great diversities of structure in the genera of 

 Ascidians, representing, in fact, almost every known tissue. Thus in 



