44 DIATOMS 
This highly interesting phenomenon can be readily observed, 
as this species is very abundant.’’ Their maximum speed 
is given as the two hundredth of an inch—the average 
length of Diatoins—a second; aud, insignificant as that 
may seem, ii we measure the speed per second of the swift- 
est ship afloat, computing that speed by the same measur- 
ing unit—her own length—as the standard, the comparison 
will be in favor of the Diatom for swiftness. 
Most of the Diatomacez are found with free separate 
frustules. But many species are held together in loose 
chaius by slight points of contact ; or are arranged side by 
side like a thread of confervae; or are fastened to a hair- 
like fixed stipe; or are imbedded in transparent glair. 
Sometimes larger numbers comprising a score of different 
species are found together in one patch of glair. Raben- 
horst found more free frustules in autumn, and more 
attached colonies in spring. “The early microscopists 
named the Diatomacez: after three modes of growth and 
their habitat. Still, their life-history being imperfectly 
known, specific names were sometimes given to organisms 
that were transitory forms of immature life. ‘The nomen- 
clature of Prof. Smith is based on particulars of the frus- 
tule and its markings. His system, if artificial, is most 
convenient. With slight additions it was adopted by Dr. 
Heurck in his synopsis of the Diatoms of Belgium, ‘The 
genus navicula includes 243 species—more than a sixth of 
those in the North American synopsis. 
Diatoms, like their next of kin, the Desmids, repro- 
duce themselves by conjugation ; and like many unicellular 
forms of life they also multiply by fission. Increase by 
fission has been carefully watched. The time from incep- 
tion of the process to complete fission is about six days. 
Particulars of these processes are given iv the Micrographic 
dictionary and in other text books. How long a Diatom 
can live is uncertain. Wolle says tiat Diatoms kept in 
water have been known to live nearly a quarter of a 
