12 NOTES AND COMMENTS [january 



Variation in a Sea-Anemone. 



Me. G. H. Parkek has sent us a note on " The Mesenteries and 

 Siphonoglyphs of Metridium marginatum'' extracted from the Bulletin 

 of the Museum of Comparative Zoology at Harvard (xxx. No. 5). 



A second title for this important little paper might have been " A 

 Warning." 



The more we learn about the fixed or sedentary forms of animal 

 life the more difficult does it become to separate the species by 

 characters which can be relied upon as being tolerably constant. 

 Many new species, new genera, and indeed some new families must 

 inevitably be unmade again, when we know more about the limits 

 of possible variations which may occur among the zoophytes. The 

 results of Mr. Parker's observations on the single species of sea- 

 anemone {Metridium marginatum) bring home to us more emphatically 

 than any previously published papers the hazardous nature of the risk 

 we run in proposing a new specific name for an anemone on the strength 

 of the examination of a single specimen or indeed of half a dozen. 



The group Hexactinia to which Metridium belongs was until 

 recently supposed to possess two of the ciliated grooves, termed 

 siphonoglyphs ; but in Metridium only 4 1 per cent were diglyphic 

 while 59 per cent were monoglyphic. Again, the name Hexactinia 

 implies a certain constancy in the number of the pairs of mesenteries, 

 but in Metridium there may be any number from three to eleven pairs, 

 and one indeed was found with as many as fourteen pairs. 



It is not necessary to follow Mr. Parker further into his statistics. 

 It is an important contribution to the study of variations he has sent 

 to us, and may have arrived in time to serve as a useful warning to 

 those engaged in the systematic study of the sea-anemones. 



Sensitive Protoplasm in Plants. 



The streaming movement of the protoplasm in the internodal cells of 

 Chara with which botanical students are familiar, is the subject of a 

 recent paper by Dr. Georg Hormann, issued in book form by Mr. G. 

 Fischer of Jena, under the title " Studien liber die Protopiasmastromung 

 bei den Characeen " (79 pp., with 12 figures; price 2 marks). Dr. 

 Hormann has studied the arrangement of the currents in the various 

 parts of the plant — leaf, root, and cortical cells — their relation to cell- 

 division and their behaviour under various external stimuli — mechanical, 

 thermal, electrical, and others. From its behaviour to electrical stimuli 

 and comparison with the behaviour of muscle and nerve fibres, the 

 author concludes that the stimulus-conducting substance in a cell of 

 Nitella, and in a fibre of nerve or muscle, contains a common fundamental 

 structural item. The nerve fibre substance is purely conductive ; that 

 in the Nitella cell is associated with a streaming mechanism, that in 

 the muscle fibre with a contractive mechanism. 



