KEPORT ON THE DIATOMACEiE. 81 



It has already been observed that in some living species of C/wetoceros, Goniothecia 

 in embryonic stages occurred, and for this reason Brightwell, 1 by analogy, has main- 

 tained that the three above-named genera are not organisms per se, but dependent and 

 subordinate parts of species of Chwtoceros. 



In confirmation of this conclusion, I have repeatedly observed conditions such as are 

 represented on Plate XIX. figs. 7 and 8, in which there may be seen frustules of Dicladia 

 capreolus, Ehrenb., 5 enclosed in frustules of Chcetoceros, and as no substantial difference 

 is found between Dicladia and Syndendrium, the non-independent character of these 

 genera is manifest. But what can be the significance of this singular organic siliceous 

 body enclosed in a Diatom cell, and itself constituting another cell ? It would seem as 

 if its sporangial nature was beyond doubt, and it must accordingly be regarded as designed 

 for the reproduction of the species. 



This interpretation of the so-called Dicladia, Gonioihecium, and Syndendrium, is 

 a confirmation of the opinion of Dr Wallich, who, instead of, like some others, viewing 

 the sporangial frustule as a means of restoring to its original dimensions a Diatom which 

 had been diminished in size by successive divisional processes, viewed it not as a normal 

 and independent organism, but as a transient monstrous form designed for the elaboration 

 of sporules or embryonal forms, and therefore capable of reproducing the species. 



" In fact it had been observed that every species, by the process of conjugation, must 

 be represented under two forms, one large and the other small, between which a gap 

 exists, over which we have at present no means of bridging except by supposing that the 

 two halves formed in cell division need not always be equal, and that by dwindling away 

 through a succession of steps of this kind, the progeny of the sporangial frustules may be 

 reduced to the original size." But that this does not happen may be shown by recalling 

 what takes place in Cocconema, Ehrenb., in a collection of which it is easy to observe the 

 sporangial, accompanied by the normal and much smaller form, without being able at the 

 same time to recognise the gradual diminution of the frustules by which the extreme 

 dimensions are reunited. (See vol. i. pi. xxiii., and vol. ii. pi. C, Synopsis of the British 

 Diatomacese.) Moreover, the same fact is shown in a still more convincing manner by an 

 observation made by Prof. Hamilton L. Smith on the Stauroneis gracilis of Ehrenberg. 3 

 This well-known naturalist recognised that the sporangial form is the same as that which 

 Ehrenberg called Stauroneis phoenicentcron * — a type which greatly differs from the former 

 in the delicacy of its striation, so that, instead of being regarded as a specific and 

 independent form, the latter must be looked upon as but a transitory reproductive form 

 of Stauroneis gracilis, Ehrenb. 



1 Brightwell, Quart. Journ. Micr.Sci., vol. iv. pp. 105-109, pi. vii. figs. 53-60. 



2 Ehrenberg, Mikrogeologie, pi. xxxv. A. 17, fig. 8. 



3 Ehrenberg, in Kiitzing's Bacill., pL xxix. fig. 3 ; Smith, Synopsis of the British Diatomaceae, vol. i. p. 59, 

 pi. xix. fig. 186. 



4 Kiitzing's Bacill., pi. iii. fig. 53 ; = Navicula phoznicenteron, Ehrenberg Infus. pi. xiii. fig. 1 ; Smith, op. 

 tit., vol. i. p. 59, pi. xix. fig. 185. 



(bot. chall. exp. — part iv. — 1886.) 1) 11 



