NAVICUIvA SOCIALIS. 1 19 



been studied by Mr. Thwaites and others. Now this part of 

 the cycle is quite unknown in the case of A'', socialis ; and as 

 the grouping is exceptional, very probably the process that 

 leads to it will be found not quite identical at every point 

 with any of those already described. My suggestion is this : — 



On reaching the minimum length, which so far as observed 

 is 60/i., the diatoms of a given group throw off their valves 

 and enter the sporing condition. At this stage they may 

 appear as a small mass of jelly containing amber-colored 

 bodies and bedecked on the surface with the cast-off valves. 

 The number of amber-colored bodies may be at first four, or 

 eight, or b}' a bare possibility a multitude, according to the 

 plan of reproduction which is followed. I suppose, however, 

 that ultimately, either with or without conjugation, certain 

 rather large spores are formed, each surrounded by its own 

 gelatinous envelope, which may be called zygospores or aux- 

 ospores, in accordance with their history. Each spore then 

 divides first into two halves, and these halves again subdivide 

 once, so that four bodies are produced after the manner of 

 Tetrasp07'a. These four final spores, still within a common 

 gelatinous sheath, then shape themselves into four new and 

 full-sized diatoms ; and having aligned themselves into a 

 typical group, still surrounded by the jelly — which now 

 becomes more thin and functions as the coleoderm — they 

 move off to meet their further destiny as A^. socialis again. 



This tetraspore conception seems the only obvious hypo- 

 thesis at present. Its correctness may be most hopefully 

 tested where the species is found growing in real abundance 

 in some sheltered water close at hand, where the full circle of 

 development may be followed continuously. Rank growth 

 under such conditions I have not yet seen, and the richest 

 gatherings so far are from the far-away Fall Mountain, in 

 Connecticut.* However, I have happened to see a few bodies 

 which may easily have been the spores of this species. They 



*Mr. W. A. Terrv. 



