234 THE FORMS OF CELLS [ch. 



naturally, however, is sometimes interrupted and disturbed owing 

 to a slight want of homogeneity in the secreted fluid ; and the 

 same phenomenon is repeated on a grosser scale when the web is 

 bespangled with dew, and every thread bestrung with pearls 

 innumerable. To the older naturalists, these regularly arranged 

 and beautifully formed globules on the spider's web were a cause 

 of great wonder and admiration. Blackwall, counting some 

 twenty globules in a tenth of an inch, calculated that a large 

 garden-spider's web comprised about 120,000 globules ; the net 

 was spun and finished in about forty minutes, and Blackwall was 

 evidently filled with astonishment at the skill and quickness with 

 which the spider manufactured these little beads. And no wonder, 

 for according to the above estimate they had to be made at the 

 rate of about 50 per second*. 



The little delicate beads which stud the long thin pseudopodia 

 of a foraminifer, such as Gromia, or which in like manner appear 



Fig. 69. Hair of Tnanea, in gtycerine. (After Berthold.) 



upon the cylindrical film of protoplasm which covers the long 

 radiating spicules of 6'^o6i^e>ma, represent an identical phenomenon. 

 Indeed there are many cases, in which we may study in a proto- 

 plasmic filament the whole process of formation of such beads. 

 If we squeeze out on to a slide the viscid contents of a mistletoe 

 berry, the long sticky threads into which the substance runs shew 

 the whole phenomenon particularly well. Another way to 

 demonstrate it was noticed many years ago by Hofmeister and 

 afterwards explained by Berthold. The hairs of certain water- 

 plants, such as Hydrocharis or Trianea, constitute very long cylin- 

 drical cells, the protoplasm being supported, and maintained in 

 equilibrium by its contact with the cell-wall. But if we immerse 

 the filament in some dense fluid, a little sugar-solution for instance, 

 or dilute glycerine, the cell-sap tends to diffuse outwards, the proto- 

 plasm parts company with its surrounding and supporting wall, 



* J. Blackwall, Spiders of Great Britain (Ray Society), 1859, p. 10; Trans. 

 Linn. Soc. xvi, p. 477, 1833. 



