166 NOTES AND MEMORANDA. 



state of tonus, or continual semi-tension. This state gives place to a 

 relaxation of tlie muscles as soon as the nerves are cut ; these latter 

 then continually transmit to the periphery a certain amount of nervous 

 influence, emanating from the nervous centres. The physiological 

 centre of these movements of the muscles of the chromatophores is in 

 the sub-oesophageal nervous mass, for the ablation of the supra- 

 cesophageal mass does not produce the decoloration. 



The contractility of the dilator muscles of the chromatophores 

 may also be set in action by irritating the skin (after the section of 

 the nerves) by electricity, heat, or a di*op of acid, or by mechanical 

 friction, which produces a dark spot. 



The action of a very bright light has an entirely opposite effect ; 

 it makes those portions of the skin on which it acts grow pale. 



The dark-coloured phase, therefore, represents the condition of 

 activity of the muscles of the chromatophores. The phase of de- 

 coloration represents the passive condition of withdrawal of the 

 chromatophores. 



The results of these experiments thus establish the accuracy of the 

 generally admitted conception of the histological structure of the 

 chromatophore, and confirm the muscular nature of the radiating fibres 

 of these elements. 



New Classification of Thallophytes. — The classification of Thal- 

 lophytes recently promulgated by Sachs,* is considered by Dr. G. 

 Winter f to be unsatisfactory in many points. Independently of minor 

 details, such as the location of Volvox among Zygosporeae, of Characeas 

 among Carposporete, &c., he objects to the main principle of the 

 classification, the abolition of the hitherto recognized classes of Alga3 

 and Fungi, and the establishment in their place of four classes of 

 Thallophytes, each consisting of a series containing chlorophyll, and 

 one destitute of it. It is impossible to maintain in many cases a near 

 genetic connection between groups placed by Sachs in two series of 

 the same class ; as, for instance, between Zygnemete and Mucorini'; 

 Vaucheria and Peronospora ; Florideee and Ascomycetes, &c. Ho 

 considers the fundamental error, both in this classification and in that 

 proposed by Cohn, to consist in laying too great stress on a single 

 character, the mode of reproduction, to the exclusion of others ; and 

 proposes to retain the primary classification of Thallophytes into 

 Fungi and Algas. The former he divides into Schizomycetes, 

 Saccharomycetes, Myxomycetes, Zygomycetes, Chytridiaceae, and 

 Oomycetes (Basidiomycetes and Ascomycetes) ; the latter into Cyano- 

 phyceaB, Chlorosporeae (including Pandorinefe, Conjugatfe, Vaucheria, 

 Volvocincce, CEdogoniefB, Coleochcete, &c.), Fucoideas, and Florideas. 

 The Basidiomycetes are divided into six families : — the Ento- 

 mophthoreae (reproduced by basidiospores with secondary spores, and 

 gonidia or gemmae), Ustilagineae (spores and sporidia, as well as 

 conidia), Uredineae (teleuto-spores and sporidia, as well as conidia or 

 Uredo), Tremellinefe (basidiospores with sporidia, and spermatia or 



* ' Lehrbuch del' Botanik,' 4th ed., p. 248 ; see also Thiseltou-Dyer, iu ' Quart. 

 Joum. Micr. Sci.,' vol. xv. (1875) p. 295. 

 t 'Hedwigia,' 1871), p. 1. 



