of the Fishery Board for Scotland. 



217 



During summer, I made a long series of attempts to discover whether 

 the species of Ceratium, then so abundant in the sea, furnished a con- 

 stituent of the food of small Crustacea, but without result. In the first 

 place, Ceratium could hardly be traced so easily as diatoms, and the 

 matter is one of difficulty. Direct observations also yielded no result. 

 I made an estimate of the relative abundance of diatoms, of species of 

 Ceratium, and of animal life in all the captures, and I found a certain 

 constancy in the proportions in the great majority of cases. When there 

 were plenty of diatoms, there were always plenty of Crustacea ; when 

 Ceratium predominated, and diatoms were scarce, there was little animal 

 life. (In Loch Fyne, in July, I made two almost pure captures of 

 Ceratium Tripos — merely one or two diatoms and copepoda mixed with 

 it.) These facts, however, are merely suggestive. There is one more 

 suggestion I should like to make. The spines of Ceratium may be a 

 protection against being eaten. I could not fail to remark that there 

 were no traces of spiny diatoms, such as the species of Chcetoceros, having 

 been eaten by small Crustacea, though they were abundant in the sea. 

 Against these negative observations, however, may be placed the fact that 

 I found Chwtoceros in the young sand-eels. Though one can suggest 

 other uses for the spines and sharp projections of diatoms, especially the 

 hollow spines of Chcetoceros, it may yet be that they are a defence against 

 Crustacea, etc., as well, and this may be equally true of Ceratium. At all 

 events, I failed to find evidence of Ceratium being eaten, though it was 

 diligently sought for ; and repeated observations and estimates appeared 

 to point to there being a balance between the quantities of diatoms and 

 animals, irrespective of Ceratium. 



Reproduction of Diatoms. — In the ordinary process of reproduction, 

 a diatom cell divides into two cells, which resemble the parent ; and, in 

 most cases, the successive generations remain attached to each other in 

 chains of individuals. Since the division takes place at the girdle where 

 one half of the wall overlaps the other, and each succeeding generation is 

 similarly overlaped, and since (unless, perhaps, in a free state) there is no 

 subsequent superficial growth, each succeeding generation is diminished 

 in size by the thickness of the girdle membrane. When a minimum size 

 is reached, diatoms become re-established at the maximum by the form- 

 ation (in various ways) of auxospores. Mr Comber has called attention 

 (Jour. Roy. Micr. Soe., October 1896) to the formation in certain diatoms 

 of 'Endocysts' resulting in the production of a dimorphic form, and Prof. 

 Cleve has recorded the presence of a specimen of Biddulphia aurita 

 within another, — the internal one being considerably smaller, and having 

 no spines (Bihang till K. Svenska Vet. Akacl. Handlingar, Bd I., No. 13). 

 Besides these modes of reproduction, nothing was certainly known of any 

 mode of multiplication until the observations I was enabled to make in 

 spring and summer on board the ' Garland.' The minute botanical details 

 and considerations have been discussed at length in a paper published, 

 by permission of the Board, in the Proceedings of the Royal Society of 

 Edinburgh (vol. xxi. p. 207. plates i.-iii.). 



It was discovered in Biddulphia mobiliensis that the cell-contents con- 

 tract and round themselves off, this more or less spherical body proceeding 

 to secrete a membrane of approximately the same shape as the parent, but 

 without the characteristic external spines, etc. This body is apparently 

 of the same character as that recorded by Prof. Cleve in B. aurita 



by chlorophyll granules, the same appearing in the foecal pellets, both in the intes- 

 tine and when discharged. " I regret that his observation was unknown to me, and 

 that I therefore did not cite it in my paper in Proc. Roy. Soc, Edin. The main point, 

 however, is the full and complete establishment of the truth ; and, since my observations 

 were made in entire ignorance of his, this confirmation is all the more satisfactory]. 



