458 ANIMAL NATURE OF DIATOMUJ3. 



Icea, Homeocladia, Schizonema, Micromega, and Dickiea) 

 constitute the group of Schizonemeae. The substance 

 which surrounds and includes the Naviculse in these 

 genera, which seems to be the same as the peduncle in 

 Achnanthides, Podosirce, and many other genera, is termed 

 jelly (gelinea), by Kiitzing, who, under this denomination, 

 compares it to that of the true Algae. The observations 

 adduced in the preceding memoir confirm the absence 

 of nitrogen, and its ternary composition. Now we know, 

 from the observations of Schmidt, Lcewig, and Kolliker, 

 that a similar substance, destitute of nitrogen, ternary, 

 insoluble in caustic potash, and isomeric with starch, con- 

 stitutes the external coriaceous stratum in the Ascidia, 

 simple and aggregate, and forms the gelatinous mass in 

 which groups of individuals of compound Ascidia are 

 lodged. These authors found that the presence of this 

 substance is a character common to all the Tunicata, 

 and it is supposed that the Doliolum mediterraneum 

 ought to be placed in the same family from this 

 character. This discovery, which I before supposed 

 possible, has therefore now entered the domain of science. 

 As the presence of a quaternary azotised substance is 

 no exclusive character of animal nature, so the pre- 

 sence of a ternary non-azotised substance, isoraeric with 

 starch, is no more an exclusive character of a vegetable 

 nature. 



With respect to origin and formation of this substance, 

 it is undecided whether, as Kiitzing asserts, we are to 

 regard it as a product of secretion, or rather as existing 

 per se. All animal secretions are formed in the same 

 manner. The theory of Goodsir, Bowman, Henle and 

 Mandl has recently received confirmation from the labours 

 of Lereboullet on the biliary vessels of the Aselli and 

 those of Gros on the production of butyraceous vesicles 

 on the internal surface of the mammary utricles. It is 

 now proved that whatsoever the animal secretions may 

 be, they are effectuated by a production of new cells on 

 the secreting surface, and the accumulation of liquid 



