HARDWICKE'S SCIENCE-GOSSIP. 



25 



EARLY HISTORY OF THE DIATOMACE^. 



By F. KITTON, Hon, F.R.M.S. 



IContinued froTtt page 9.] 



IGHT has great in- 

 fluence on various 

 species oi Navicii- 

 la and Frnstulia, 

 and when they are 

 kept in cylindrical 

 glass jars they al- 

 ways attach them- 

 selves to the side 

 nearest the light, 

 leaving that which 

 is dark. I therefore 

 always search on 

 the light-side for 

 the finest speci- 

 mens : kept in 

 porcelain vessels 

 filled with water, 

 and exposed to the 

 light, they rise to 

 the surface of the 

 %vater. Siirirella Vemis (fig. S) generally keeps its 

 cuirass a a closed during the day, when the opening 

 is only seen in dead individuals ; during the night 

 and by very feeble lamp-light I have found many 

 open, but they quickly closed when exposed to a 

 more intense illumination. 



Organs of Nutrifion. — Nutrition and the organs 

 necessary for that purpose, are extremely difficult to 

 detect ; we cannot adopt the means that enabled 

 Ehrenberg to examine the true infusoria, seeing that 

 the animalcules with which we are now occupied are 

 unable to admit colouring substances. It is therefore 

 only analogy that can assist us (and that very feebly) 

 in these researches. 



In the Surirellas and Naviculas I have never been 

 able to detect the parallel tube in the body. In 

 Surirella Venus (fig. 8) we can easily perceive a skin 

 separated from one of the points of the mantle ; this 

 skin shows a slit a which leads to the contents e ; by 

 means of this slit the animal can eject the whole of 

 them, but I have never been able to detect any 

 aperture or cleft in the mantle. 

 No. 206.— February 1882. 



The Naviculas, according to my arrangement, in- 

 clude the species of the older genera of Friistidia and 

 Naviaila in which we find on the pedal surface two 

 apertures at the axes of the body, leading to two 

 empty tubes which traverse the entire length of the 

 animalcule, and which terminate at the two openings 

 close to the smooth pedal surface. 



The genus Pharyngoglossa is the only one of the 

 series in which may be distinctly seen the mouth, the 

 alimentary canal, and its anal aperture. The head is 

 easily recognised by the fissure in the cuirass, from 

 which the superior foot is extended ; below this foot 

 is an orifice in which may be seen a plug which it 

 protrudes, this plug forms a part of the cylindrical 

 bowel, which becomes very delicate as it approaches 

 the posterior part of the body, and terminates at the 

 orifice in the cuirass, and through which the hinder 

 foot is extended. 



Pharyngoglossa is also the only form of this class 

 in which I have seen the ingestion of solid matter, 

 which, when the plug is extended, rushes into the 

 empty space (fig. 4) between what we, from analogy, 

 have called the mouth and stopper. In speaking of 

 the intestines, we alluded to the coloured substance in 

 the animalcules, enclosed in the mantle ; this is some- 

 what peculiar in its constitution and colour. In gene- 

 ral this matter appears to be gelatinous, semi-liquid, 

 homogeneous, containing drops of oil or fat, and verj' 

 minute granules of solid matter. In Surirella Venus 

 it forms a green or brown granular mass in the centre 

 of the animalcule ; in Naviculas, Frustulias, and in 

 some Diatoms, this mass is spread out into a thin 

 layer, coloured and curved at the margin towards the 

 base, and which after the death of the animalcule 

 becomes irregular. 



The genus Scalptrum and some species of Namciila " 

 (undescribed) have the power of expelling the coloured 

 contents through the opening we see on the ventral 

 surface, they also appear to possess the power of 

 reproducing these contents. 



In the Diatoms and Fragilarias, we also detect 

 this internal material excepting at the extremities of 

 the body which are in consequence transparent In 



c 



