The Structure of Diatoms. By Dr. J. H. L. FUgel 689 



Plates X. and XI. 



Figs. 33-52. — Achnanthes brevipes. 



m k, central node. 



d s, dorsal valve. 



V s, ventral valve. 



r I, marginal ridge (r l' old, r I" young). 



g 5, girdle-band. 



s z, marginal view of the same. 



Fig. 33 X 670. — A chain consisting of two young frustules. The cell on the 

 left is figured in full detail in the manner usually adopted in representing diatoms ; 

 i. e. by focusing as a whole. The cell on the right is naturally similarly con- 

 ditioned. The transverse lines are only indicated, but for the central part the 

 highest focus has been chosen for the representation ; it brings to view the 

 marginal striae s z' of the old girdle-band. Further on towards the edge it is 

 focused a little lower ; then only are seen the very short dotted strise s z" of the 

 young girdle-band between the two marginal ridges. In the cell on the right, 

 near one end, the young ridge has separated considerably more from the old 

 one than at the other end. The numbers refer to the direction of the sections, 

 figs. 40-2. 



Fig. 34. — The upper edge of the preceding fig. under exact medium focus. 

 The marginal ridge shows a saddle-shaped depression, the small elevation is the 

 young ridge in process of splitting away from the old one. The depression 

 between the two must be looked upon as the first visible indication of the young 

 girdle-band. The old girdle-bands extend one over the other only in the 

 direction s. The cells are without doubt completely closed. The girdle-band is 

 raised at the marginal ridge slightly. Marking of the surface view given with 

 the valves below. 



Fig. 35 X 670. — A chain similar to the preceding, but a little older ,■ the 

 young marginal ridges r I" are further apart from the older r I'. Only the strise 

 of the young girdle-band s z" are represented. 



Fig. 36. — The upper edge of the left ceil in fig. 35, in order to bring to view 

 the relation between the two marginal ridges and the doubly thick membrane 

 between them. 



Fig. 37 X 670. — An older cell, probably shortly before division. The peculiarly 

 interrupted striated marking of the girdle bands is given. Tliis is about the 

 most complicated striation of all ; between this and fig. 35 one finds all transitions. 

 It seems as though the boxed-up girdle-band had already separated from its 

 marginal ridge. 



Fig. 38 X 670. — A dorsal valve and 



Fig. 39 X 670. — A ventral valve viewed from the surface with full marking. 



Fig. 40 X 660. — Transverse section No. 1, 

 „ 41 „ „ 5, and 



,. 42 „ „ 15 



out of a series of 23. They correspond to the dotted lines 1, 2, 3 in fig. 33 

 (naturally with the modification that we have here to do with a chain of three 

 frustules). Fig. 40, extreme marginal section which has touched only one 

 portion of the lowest cell. Fig. 41, the middle cell partially injiured in cutting. 

 Fig. 42, the uppermost cell crumbled out. 



Fig. 43. — Transverse section No. 12 of the same series. The uppermost cell 

 quite uninjured. Quite distinctly is here observable the difierence in size between 

 the old (>• I') and the young (r I") marginal ridge ; the hook shape of the former 

 also visible. The valve membrane is distinctly dotted (as expression of the dots 

 between the tran-sverse lines in the surface image), m r, mid-rib.s. 



Fig. 44. — Portion of the same uppermost cell from the transverse section 

 No. 9 of this series. The adjoining cell is split oft" whereby the duplex of the 



firdle-band becomes distinct, because in consequence of the fracture both mem- 

 ranes have separated ; rj h' the old, g h" the younger girdle-band. 

 Fig. 45. — Portion of the ventral valve of this uppermost cell to show the mid- 

 rib mr and the hurrounding fine spaces as in the sections Nos. 8 and 16 of the 

 alxjve scries. The fine line <] is tlic inner limit of one of the transverse striae. 



