THE STRUCTURE OF PROTOPLASM. 7 



from the optical section of "alveolar" or emulsion-structure. 

 The spaces of the meshwork are drops of liquid occupying 

 spherical spaces or " alveoli " ; the " fibres " are optical sections 

 of the thin layers, or lamellae, by which the drops, or alveoli, 

 are surrounded. Even the astral systems receive the same 

 interpretation, the astral "rays" and "spindle-fibres" being 

 an optical illusion resulting from the radial arrangement of 

 the alveoli, and hence of the inter-alveolar septa by which they 

 are separated. 



The greater number of observers of protoplasm have given 

 their adherence to one or the other of the two widely dissimilar 

 views just outlined, though there are others to which we shall 

 return later. Some investigators have taken a position inter- 

 mediate between these two extremes. Thus Reinke has main- 

 tained that the cytoplasm of the echinoderm-egg is alveolar, 

 as described by Biitschli (though, as will appear beyond, he 

 ascribes to this structure a different physiological interpreta- 

 tion), while the astral systems are fibrillar, as held by Van 

 Beneden, and arise as new formations at the cost of the alveolar 

 walls. More recently, Strasburger has developed the related, 

 but still different, view that the cytoplasm of the cell at large 

 consists of two distinct substances, namely, the ti'ophoplasm, or 

 general nutritive plasma, which is alveolar, and the kinoplasm, 

 or the substance active in division, which is fibrillar and gives 

 rise to astral systems consisting of true rays and fibres. 



It is remarkable that the best observers, working in many 

 cases at the same object, should have reached conclusions so 

 diverse. It is obvious, further, that in the face of such contra- 

 dictions it is impossible to give any discussion of the subject 

 that is not more or less strongly tinged with the personal views 

 of the writer. Such views, by whomsoever expressed, can at 

 present have no more than a provisional value ; and this is the 

 last subject on which dogmatism should be allowed. It is with 

 full recognition of these difficulties that I venture to state some 

 of my own conclusions, partly because they may serve to explain, 

 in some measure, to those who have not specialized in this field, 

 how the existing diversity of opinion has arisen, partly because 

 they have perhaps some bearing on the more general questions 



