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Part III. — Fifteenth Annual Report 



(of which I was ignorant at the time). During summer, I found these 

 internal bodies free in the water in large numbers, and in a state of active 

 division, none of them having developed the characteristic external spines 

 of the parent form. The parent form was almost wholly absent. In 

 December, again, the parent form (with spines) was abundant, but none of 

 the summer forms. Presumably these had grown into mature Biddidjphia 

 mobiliensis, either directly, as is most likely, or after some other develop- 

 ment. The production of this internal form, so far as I have seen, in 

 Bidduljphia, is always a case of rejuvenescence of the cell, the whole of 

 the cell-contents of the parent being used up in the formation of one new 

 cell, which, when free, increases its kind by division. I have observed 

 similar rounding off in the cell-contents of Ditylum Brightivellii, and very 

 probably it goes through a similar life-history. 



In Cosciuodiscus concinnus, I have also found a young form within the 

 parent, this time exactly resembling it in all essential characters. In this 

 genus also, therefore, we have the production of a new individual by the 

 rejuvenescence of the cell. That this often happens in spring I had 

 abundant evidence ; but, what is more interesting, I have found in this 

 species two diatoms within the parent, showing that the protoplasm must 

 have divided to form them. In Loch Fyne I found other specimens of 

 0. concinnus, of which the protoplasm had divided into four, eight, and 

 sixteen rounded-off portions (produced to judge by their positions, etc., by 

 successive divisions into two) ; and free in the water at the same time, 

 packets of eight and of sixteen young Cosciuodiscus concinnus, of the same 

 size as the rounded portions of protoplasm. The conclusion was inevi- 

 table that the packets of eight and of sixteen were produced from the 

 rounded-off portions, having regard to the occurrence of single forms and 

 pairs as described above. The membranes of the young individuals were 

 either not silicified, or were imperfectly silicified, as proved by burning ; 

 and they were therefore capable of growth, and of attaining the full 

 dimensions of Cosciuodiscus concinnus, without the intervention of auxo- 

 spores. 



Both in spring and summer, I observed in several species of Chcetoceros 

 a series of divisions of the cell-contents, obviously similar to the divisions 

 in Cosciuodiscus, and doubtless preliminary to the formation of repro- 

 ductive bodies. In C. borealis this sub-division of the contents is carried to 

 four, eight, and sixteen ; in C. curvisetus to four and eight ; and in C. con- 

 strictus to four. Instances of higher numbers in the latter two species may 

 and probably do occur, but they have escaped me. I have witnessed the 

 actual processes of division up to four ; but the farther sub-divisions into 

 eight and into sixteen are known to me only from finding instances of 

 them as accomplished facts. What the fate of these bodies may be I do 

 not yet know, but I hazard the view that they resemble the corresponding 

 bodies in Cosciuodiscus in their life-history. 



Having obtained a supply of sea-water, I am endeavouring to cultivate 

 these organisms during the winter in two large tanks, and, if possible, to 

 secure a continuous series of observations. There are enormous difficulties 

 in cultivating such organisms in London, but so far I have a prospect of 

 success. 



There are numerous questions of both scientific and economic import- 

 ance to be settled in connection with the study of marine vegetation. 

 That little is known may be inferred from the fact that it was possible to 

 make so many novel observations within so short a time. I would venture 

 to recommend to the Board that a survey of the conditions be made 

 farther out at sea, that we may know how far these banks of diatoms, 

 Peridinieae, etc., extend seawards, especially in the early months of the 

 year and in summer, or how far they may be coastal in their occurrence. 



