10 Mr. G. H. K. Thwaites on Conjugation in the Diatomacese. 



I have just had the good fortune to make, of Eunotia turgida, 

 Ehrh., a species belonging to the natural family Diatomacece, in 

 a state of conjugation, — a discovery which is valuable as proving 

 that a relationship of affinity, as well as of analogy, exists between 

 the Diatomacece and the Desmidiea and Conjugates, and which 

 will help to settle the question as to whether the former are to 

 be referred to the animal or the vegetable kingdom. 



The Eunotia turgida is not very uncommon in ditches, and is 

 generally attached by its concave surface to the filaments of va- 

 rious freshwater Algae. Plate IV. fig. 1 is a magnified view of 

 this surface, and fig. 2 represents the side-view of a frustule. The 

 process of conjugation in this, as in the species of the natural 

 family Desmidiece, consists in the union of the endochrome of two 

 approximated fronds, this mixed endochrome developing around 

 itself a proper membrane, and thus becoming converted into the 

 sporangium. In a very early stage of the process the conjugated 

 frustules of the Eunotia have their concave surfaces in nearly close 

 apposition (fig. 3), and it may be observed, that from each of these 

 surfaces two protuberances arise which meet two similar ones in 

 the opposite frustule: these protuberances indicate the future 

 channels of communication by which the endochrome of the two 

 frustules becomes united, as well as the spot where is subse- 

 quently developed the double sporangium, or rather the two 

 sporangia. A front view of the conjugated frustules at the same 

 period (fig. 4) shows each of these to have divided longitudinally 

 into two halves, which, though some distance apart, are still held 

 together by a very delicate membrane, that however soon dis- 

 appears. 



The mixed endochrome occurs at first as two irregular masses 

 between the connected frustules, but these masses shortly become 

 covered each with a smooth cylindrical membrane — the young 

 sporangia (figs. 5 & 6) — which gradually increase in length, re- 

 taining nearly a cylindrical form, until they far exceed in dimen- 

 sion the parent frustules (fig. 7), and at length when mature be- 

 come, like these, transversely striated upon the surface (fig. 8). 

 Around the whole structure a considerable quantity of mucus has 

 during this time been developed by which the empty frustules are 

 held attached to the sporangia. 



I may add, that in a species of Gomphonema, allied to G. di- 

 chotomum, I have observed the first appearance of conjugation, 

 which I hope to be able to trace to the perfect development of 

 the sporangia. 



I am, Gentlemen, your very obedient servant, 



Geo. H. K. Thwaites. 



June 12, 1847. Since my last communication on the sub- 



