BRITISH TUNICATA. 



forms that it appears impossible to give to that group 

 any definite boundaries. Milne-Edwards' paper is 

 beautifully illustrated with coloured plates. 



In the year 1845 Schmidt, in his work ' Zur verg- 

 leichenden Physiologic der wirbellosen Thiere,' made 

 known the startling discovery that cellulose was a 

 constituent of the test oiAsciilln or Phallusia mamillaris. 

 Lowig and Kolliker [in 'Ann. Sci. Xat.' (3), v] con- 

 firmed the statement of this distinguished naturalist, and 

 ascertained that this substance was present in the outer 

 envelope of different species of the genera Phallusia, 

 Ci/iifliin, Cl<rreUii/<f, Vin::<>ii<i, Aplidium, Didemnum, 

 Botnjllus, I'l/i'nxnnia, and Snlpa, so there can be no doubt 

 that cellulose is a constituent portion of the whole of 

 the Tunicata. 



AYithin the last few years several other important 

 papers have appeared on the structure and develop- 

 ment of the various forms of these animals, amongst 

 which must be mentioned a memoir on the embryology, 

 anatomy, and physiology of the Simple Ascidians by 

 Van Beneden, published in the Memoirs of the Eoyal 

 Academy of Belgium [xx (1847)]. From 1846 to 1852 

 Krohn published several important papers on the re- 

 production and development of the Tunicata. Professor 

 Huxley's various contributions on the structure of the 

 Tunicata were also published at about this time. His 

 excellent memoirs " On the Anatomy and Physiology 

 of ftalpci and Pyi-osoma" and " On the Anatomy of 

 Appendicularia and DoUolini/," were printed in the 

 ' Philosophical Transactions ' for 1851. In the former, 

 Chamisso's facts as to 8<ilpn are tested and confirmed, 

 and the results of Krohn's paper 011 the same subject 

 are verified. Papers of high merit on the Tunicata 

 have also been published by Cams (1816-21), Eleven 

 (1832-35), Eschricht (1839-43), Steenstrup (1842), 

 Sars (1846-47), and others. 



Little was done in working out the species of the 

 Tunicata in early years ; a small number only being 

 described by a few distinguished naturalists, one of 



