BY ARTIFICIAL MEANS. 43 



in which purposely you give predominance to the physical and 

 chemical elements ; then the diatoms which grow under these 

 conditions take strange forms, and I have given to these growths 

 the name of " teratological growths." I have followed to the 

 third generation these strange variations of form ; among some 

 of the Nitzchias and Cyclotellas, nothing is more curious than to 

 see the first of these diatoms puffed out — symmetrically narrowed — 

 and become altogether unrecognisable; while as to the Cyclotellas, 

 so regularly constructed in a box-like form, you notice the valvular 

 face lose the circular forms, become oval, triangular, quadrangular, 

 or take the appearance of a closed curve, not angular, but very irregu- 

 lar; at the same time the flat surface of the circle is warped, becomes 

 hilly — the ridges of the upper and under surface of the cylinders 

 wander about forming hills and valleys — the general design of the 

 Cyclotella remains, but presents an appearance of great modi- 

 fication. These modifications of form are clearly appreciated when 

 noticed in progress, and it is not uncommon to see the box-shaped 

 diatoms appear like accordions, as if, being flexible, they had been 

 submitted to a strong pressure. This strange shape does not 

 prevent these monstrosities being lively and perfectly endochromed. 

 The results obtained by the teratological growth appear to me 

 very remarkable ; they explain in the first place why we meet in 

 nature with abnormal forms. It seems that if you could fix the 

 diatoms in the strange forms I have referred to, you might not 

 only produce an infinite variety of hybrids of the same species, 

 but perhaps also be able to follow a series of modifications that 

 might lead slowly from one species to another. I am only sure, at 

 present, as to the possibility of producing by culture important 

 changes of form in the siliceous carapaces of diatoms. I say no 

 more on this subject, which is far too important to be treated 

 here in an incidental manner. 



Mr. Conway, who is exploring in the Himalayas, finds the 

 peaks difficult in their lower parts ; the region above seventeen 

 thousand feet is easy, but in bad weather one is cut off from the 

 upper region by the next seven thousand feet below. There are 

 numerous and vast glaciers descending to between eight thousand 

 and nine thousand feet above sea level. 



