6 BRITISH MOLLUSCA. 



Physlologie cler wirbellosen Thiere," put forward the novel 

 statement, that he hail discovered in the tunic of an Asci- 

 dian molhisk (the Phallusia mammillaris) a ternary sub- 

 stance identical with celhdose. He inferred thence that no 

 chemical distinction could be drawn between animals and 

 vegetables ; and, as he had previously shewn that on no 

 other structural or physiological ground any line between 

 the two kingdoms could be drawn, he put forward the 

 somewhat bold dogma, that " Psychology only is competent 

 to trace a limit between plants and animals ; and that the 

 only difference admissible is, that the animal possesses, 

 besides the vegetable form — i. e. cellule — a -^/U);^??.'"' 



Whatever naturalists might think of Dr. Schmidt's hypo- 

 thetical definition, it became them to look to his statement 

 respecting the presence of cellulose in the Ascidian tunic. 

 Fortunately the inquiry was undertaken by two most com- 

 petent observers, Professors Lowig and Albert Kolliker : 

 the result was to confirm the statement and extend it. 

 They found cellulose undoubtedly present in the envelopes 

 of many Tunicata, both simple and compound, including 

 the genera Phallusia, Cynthia, Clavelina, Diazona, Bo- 

 tryllus, Pyrosoma, and Salpa. But they sought in vain 

 for cellulose in animals of inferior organisation, although in 

 some of the above-named creatures it formed a very consi- 

 derable part of the animal tissues.* 



The explanation offered by Lowig and Kolliker of these 

 very anomalous facts is extremely ingenious, and probably 

 very near the truth. It is to the following effect : — Tunicata 



• The memoir of MM. Liiwig and Kolliker was examined b}^ a committee of 

 the French Institute, consisting of Dumas, Milne-Edwards, Boussingault, and 

 Payen : the last-named eminent philosopher drew uj) the report. In it he gives 

 the following formula of the composition of the envelopes of the Tunicata : — 



Cellulose .... GO-34 



Azotised substance . . 27'00 



Inorganic matter . . lO'GS 



1 0000 

 He remarks that the establishment of the existence of cellulose in the Tuni- 

 cata is a " fait capital " in science, very important in its bearing on future re- 

 searches into the comparative physiology of the two kingdoms. 



