246 Transactions of the [Sess. 



The contents of the diatomaceous frustules consist of the follow- 

 ing distinct structures : (1) the soft, mucilaginous, yellowish-brown 

 or orange-brown endochrome or " gonimic substance " of Kiitzing ; 

 (2) a distinct central nuclear body, which is probably, as indicated 

 by Schleiden, the point at which, as in other organisms, fissiparous 

 division originates, and which, according to Nageli, is either pri- 

 mary (?.e., active) or secondary (i.e., inactive), and includes a 

 distinct nucleolus ; and (3) translucent globules, which, on the 

 whole, are definite and constant in position, and occupy less space 

 than that taken up by the nucleus. These globules, according 

 to Smith and Kiitzing, are fatty or oily, and have been looked 

 upon by Kiitzing as equivalent to the starch of higher vegetables ; 

 while, on the other hand, Eln-enberg regarded them as the male 

 reproductive organs of the living frustules, the vesicles in the 

 vicinity of the nucleus being regarded as " stomach sacs." Objec- 

 tions were, however, soon raised to this polygastric view, among 

 which may be noted the circumstance that colouring matter could 

 not be detected to be carried along towards the middle, where 

 these sacs should lie. The mucilaginous endochrome may be either 

 diffused irregularly in the interior of the cell, or may form parietal 

 layers or plates, or be more aggregated towards the centre, or it 

 may be dis^josed in lines radiating fiom the nucleus. The green 

 colouring matter is concealed by a buff-coloured substance called 

 " jjhycoxanthin." ^ 



Whether the miicilaginous contents of Diatom cells come into 

 actual contact with the external medium cannot yet be said to 

 be clearly decided, owing to the great difSculty experienced in 

 determining the minute structure of the cell walls. That such 

 a contact does occur along sutures between the opposed valves, 

 or between the valves and cingulum, has, however, been asserted 

 by several observers, especially by those who maintain that the 

 movement of the frustules in their watery medium is due to 

 cilia. 



To account for the movements of living Diatoms, which are often 

 of an extremely interesting and are always of a puzzling character, 

 various hypotheses have been advanced, but -no satisfactory ex- 

 planation of the phenomena has yet been forthcoming. Free as well 

 as concatenated frustules may move, and even fixed forms some- 

 times exhibit such characteristics. The motion in many cases con- 

 sists of a series of jerks in a given direction. These are followed 

 by a pause, and the frustule then returns to its original position by 

 a series of jerks in the opposite direction, and in the movement an 

 obstacle is not avoided. As, however, other undoubted vegetable or- 

 ganisms are capable of locomotion, the phenomenon cannot be looked 



1 Sachs' ' Text-Book of Butuiiy,' 2J ed., p. 260. 



