The Thallus of the Diatomacese. By F. Kition. 39 



until the thallus became charged with germs and frustules in various 

 stages of development. In this same thallus was also seen the 

 gradual transformation of the corpuscles into rudimentary frustules, 

 their growth, and lastly the development of the dichotomous 

 peduncle. When this cycle was completed, the thallus contained 

 three different forms — the sessile sphenelloid form, the pedunculate 

 (either simple or dichotomous), and the perfect or free form. From 

 the preceding, it appears that there arrives a time when the plasma 

 contained in the siliceous cells acquire a considerable volume, owing 

 to the rapid development manifested at the time of reproduction, 

 and which cannot be contained within the walls of the frustule by 

 reason of the want of elasticity produced by the deposition of silex. 

 The frustules being unable to follow the growth of the plasma, the 

 valves separate from the pressure ; but previous to arriving at this 

 condition, the protoplasm had commenced to undergo the changes 

 necessary to the formation of the new cellules, and we are able to 

 see an aggregation of hyaline masses destitute of an external 

 membrane. These are the Moneres of Haeckel. Amongst them 

 are some that remain for a long time as plastid gymnocytodes — that 

 is to say, without an external membrane, as named by Haeckel — 

 and form in this manner the amorphous or indefinite thallus 

 {mucus matriculis of authors) ; whilst those that take the form of 

 stipes, peduncles, cushions, or some definite form, appear to belong 

 to the plastid lepocytodes, that is to say, invested with an extremely 

 thin external membrane. This membrane, although scarcely visible 

 with the Microscope, nevertheless Umits the outline of the thallus. 

 ... I have determined to place the above-mentioned facts before 

 diatomists, in order to call their attention to the study of the thallus 

 of diatoms. The study of the function of the thallus in this large 

 family seems to me to be full of interest." 



The presence of this •' thallus " is by no means uncommon. 

 I have detected it in many diatomaceous gatherings, particularly 

 those from fresh water, but I never saw the corpuscles Dr. Lanzi 

 mentions ; they may not have been present, or, what is equally 

 probable, I overlooked them. However, the discovery is of great 

 interest ; and I hope, with Dr. Lanzi, that other diatomists will 

 turn their attention to the study of the living forms. The repro- 

 duction of the Diatomficea3 has not received that amount of atten- 

 tion the subject deserved. Their increase by self-division was the 

 method first observed, more careful observations led to the detection 

 of conjugation and production of sporangial frustules, or the for- 

 mation of a sporangium by a single frustule ; and we now find that 

 another method has been observed, viz. that just described by Dr. 

 Lanzi. 



The author's figure (1) represents a number of circular bodies 

 immersed in the thallus of E. rentricosa, and also in the frustule ; 



