30 LEPADID^l. 



spines, connected with the underlying corium by tubuli, 

 are not unfrequently articulated on this membrane : the 

 tubuli, however, are often present where there are no 

 spines. To allow of the growth of the capitulum, the 

 membrane between the valves splits at each period of 

 exuviation, when a new strip of membrane is formed 

 beneath, connected on each side with a fresh layer of shell, 

 — the old and outer slips of membrane disintegrating 

 and disappearing: when there are many valves, the line of 

 splitting is singularly complicated. This membrane 

 consists of chitine,* and is composed of numerous fine 

 laminae. After the valves have been placed in acid, a 

 residue, very different in bulk in different genera, is left, 

 also composed of successive laminae of chitine. It appears 

 to me that each single lamina of calcified chitine, com- 

 posing the shell, must once have been continuous with a 

 non-calcified lamina in the membrane connecting the 

 several valves : at the line where this change in calcifi- 

 cation supervenes, the chitine generally "assumes some 



* Chitine is confined to the Articulata. It was Dr. C. Schmidt (Contri- 

 butions, &c, being a Physiologico-Chemical investigation: in Taylor's 

 ' Scientific Memoirs/ vol. v), who discovered that the membrane connect- 

 ing the valves and forming the peduncle, and the tissues of the internal 

 animal, were composed of this substance. But Dr. Schmidt says that the 

 valves in Lepas are composed of 3*09 of albuminates, and 96*81 of incom- 

 bustible residue ; I cannot but think that the existence of the albuminates is 

 an error caused by Dr. Schmidt's belief that the Cirripedia were intermediate 

 between Crustacea and Mollusca, in the shells of which latter, the animal 

 basis consists of albuminates. For after placing the valves of Lepas and 

 Pollicipes in cold acid, I found that the membrane left could not be dissolved 

 in boiling caustic potash, but could, though slowly, (and without change of 

 colour,) in boiling muriatic acid ; and these are the main diagnostic charac- 

 ters of Chitine, compared with albuminous substances. I may add, that 

 Schmidt was also induced to consider the shells of Cirripedia as having the 

 same nature with those of Mollusca, from finding that in the above 96*81 of 

 incombustible matter, 99*3 consisted of carbonate and only 0*7 of phosphate of 

 lime ; but Dr. Schmidt's own analyses prove how extremely variable the pro- 

 portions of these salts are in the Crustacea, as the following instance shows : — 



Lobster. Squilla. 



Phosphate of Lime . . 12*06 . . 47*52 

 Carbonate of Lime . . 87*94 . . 52*48 



And, therefore, it is not very surprising that Cirripedia should have still 

 less phosphate of lime in their shells, than has a lobster compared with a 

 squilla. 



