218 Proceedings of Royal Society of Edinburgh. [sess. 
pollen-grains of this plant in the surface-net — objects which, among 
unicellular marine Algae, at first sight puzzled me not a little. 
In order to attempt the settlement of various questions that have 
arisen in the course of this investigation, and especially the tracing 
of life-histories by continuous observations, I have had two large 
tanks prepared for the purpose of cultivating marine diatoms, with 
the hope of overcoming the numerous difficulties that attend such 
an experiment. 
Professor Weiss, of the Owens College, Manchester, has informed 
me in a letter that he has made observations similar to some of 
those recorded here. On learning that I was working at the 
subject, he generously refrained from competition in priority of 
publication. 
In addition to work at sea, in which I have to acknowledge the 
courtesy and kindness of Captain R. Campbell of the “ Garland,” 
it has been necessary to search microscopically and to mount a vast 
quantity of preserved material, and I desire to record my thanks 
for cheerful assistance in this task to Miss Barton, Miss Frances 
Whitting, and Mr Percy Highley, who have all aided me with 
valuable suggestions and observations. I must thank Professor 
Cleve for the names of some of the diatoms. 
EXPLANATION OF PLATES. 
Plate I. 
Fig. 1. Biddulphia aurita, with young Biddulphia within it (after Cleve). 
Fig. 2. B. mobiliensis, with cell-contents rounded off. x 800. 
Fig. 3. Do., with young Biddulphia within it. x 800. 
Fig. 4. Do., young form free, x 600. 
Fig. 5. Do., dividing, x 600. 
Fig. 6. Ditylum Brightwellii , with contents rounded off. x 800. 
Fig. 7. Coscinodiscus concinnus, with one young Coscinodiscus within it. 
x 500. 
Plate II. 
Fig. 1 , a and b. Coscinodiscus concinnus , with two frustules within it. 
x 500. 
Fig. 2. Do., with contents divided into eight; a, valve-view ; b, girdle- 
view. x 500. 
