54 THE AMERICAN MONTHLY [March, 



the holes in the shell to the exterior, and without further ado there 

 settle down, put forth pseudopodia, form a stalk and fix themselves, 

 and finally silicify the protoplasmic foundations of their skeleton — in 

 fact, become directly transformed into perfect forms. 



"Another method consists in the simple or the multiple fission of 

 the protoplasmic body into a larger or smaller number of parts, which, 

 instead of leaving the shell at once and settling down as naked and 

 active bodies called amtEbulge, as in the preceding method, become en- 

 cysted, each surrounding itself with a case, the outer surface of which 

 is beset with fine siliceous spines. After a long rest, which probably 

 lasts all the winter, there is developed from each cyst one free-swim- 

 ming zoospore, or fl;igellula, which in its anterior and somewhat 

 pointed homogeneous end contains a nucleus, and in its posterior gran- 

 ular end two or more contractile vacuoles, and is furnished with a pair 

 of long, whip-like cilia, or flagella, for locomotion. The description 

 of the transformation of these flagellulaj into CIatJir2iIina will be 

 given below. 



" In a third method, the protoplasmic body divides by multiple fis- 

 sion into three — two smaller and equal and one larger equal to the other 

 two together — or rather probably into two, one of which again divides 

 into two, while the other does not, or at least has not been observed to 

 do so. The fate of the latter is not certainly known, but it may with 

 confidence be inferred that it also, in turn, divides into two, which quit 

 the shell as flagelluhe. However this may be the products of the di- 

 vision of the former half quit the shell at or about the same time by forc- 

 ing their way through the holes in its walls, and as soon as they are 

 free form fiagclhdce like those already described under the second 

 method. After swimming about for a short time with a slow, rotatory 

 movement, the young germ places itself upright upon the object to 

 which it will eventually attach its stalk, and assumes a globular form, 

 revolving the while about its own axis without change of position. 

 With the cessation of movement, pseudopodia are quickly developed on 

 all sides, and the body takes the form of an amoebula similar to that 

 with which development began in the first method. The stalk arises 

 as a process of the body substance, in which at an early stage granule 

 currents are plainly to be made out, and it is hence primitively a proto- 

 plasmic structure. Later on, the skeleton of the difinitive stalk is 

 developed upon this protoplasmic foundation, in all probability by the 

 impregnation with silica of a thin layer of exoplasm and by the subse- 

 quent withdrawal into the body substance of the fluid protoplasmic 

 core. However this may be, in the fully developed animal the stalk is 

 also an empty tube, continuous with the latticed shell. The develop- 

 ment of the latticed shell has not been fully followed, but it appears 

 probable that it, like the skeleton of the stalk, is also pre-formed in 

 protoplasm, which subsequently becomes hardened by deposit of sili- 

 ceous salts upon, or within, its substance. Thus, in the two later 

 methods of multiplication, we have a distinct metamorphosis, the young 

 difiering from the adult in form and habit ; and of the three methods, 

 those that are accompanied by a metamorphosis are the most important 

 to the species as securing its dispersal." 



