Navicula serians, N. rhomboides, and Pinnularia gibba. 173 



sequently to the impregnation of the germ-cells, might sooner 

 or later, under favourable circumstances, assume the cystic form 

 filled with embryos, described by Prof. Smith as the probable 

 ultimate destination of this sac, and actually found by him filled 

 with the embryonal frustules of Cocconema cistula, &c, in a 

 gathering of this Diatom which presented " forms of it of every 

 size intermediate between the minutest frustule in the cyst and 

 the ordinary frustules engaged in the conjugating process" (apud 

 Pritchard, p. 71). 



I have long since figured in the 'Annals' a similar termina- 

 tion to the Rhizopoda in the case of more than one Amoeba, — 

 that is to say, the parent sac or animal becoming the deciduous 

 cyst of the new progeny. 



Again, should this process of impregnation take place in the 

 Diatomea;, is it not probable that it may also be similar in Des- 

 midiese, Euglena, and Spirogyra, &c. ? 



Finally, I have now to allude to the " glair-cell " of the 

 Diatomcte, a capsuled organ so designated and described by 

 myself in 1856 (Annals, vol. xviii. p. 241, pi. 7. figs. 87-91), 

 but not previously noticed, except it be one of the bodies to 

 which the acute observation of the illustrious Berlin microsco- 

 pist, Ehrenberg, attributed a spermatic function — and never, to 

 my knowledge, since. I must thus again recur to it here, as I 

 have enumerated it among the organs of the Diatomese; and in 

 so doing I need not repeat all that has been published upwards 

 of eight years since, further than that this organ has frequently 

 the appearance of an oil-globule, and is conspicuously situated 

 towards each end of the frustule, being double. It, however, 

 differs from the oil-globule in possessing a capsule, in not being 

 of the same form in every genus of Diatomese, e. g. Amphiphora, 

 where it is skittle- or barrel-shaped (Annals, pi. 8. fig. 90, 1, c), 

 and in sometimes changing its spherical for a caudate or stellate 

 figure, in Navicula fulva, &c, when it loses much of its refractive 

 appearance; while it undergoes duplicative division with the 

 frustule just as much as the nucleus. It seems to have its 

 homologue in the Euglena, both singly and in duplicate, accord- 

 ing to the species ; but I have not observed it in any other 

 Infusoria. 



Now, if I be right in attributing a spermatic office to the 

 nucleus in Difflugia, &c, and the impregnative generation in 

 the Diatomese be produced in the same way, it then remains for 

 us to find out from what source the germ-cells are derived. 



In Difflugia I have recognized nothing like the glair-cell of 

 Diatomese, &c, and at present cannot account for the origin of 

 the supposed germ-cells there, unless they be developed from 

 the soft internal part of the sarcode ; while, if they be of the 



