222 THE NORTHERN MICROSCOPIST. 
species show regular points or designs upon the connecting 
zones. 
Reproduction by binary division occurs in this genus, in the 
usual manner, viz.: by the formation of two new valves in the 
interior of the hoop of old ones. Fig. 49 gives the view of an 
Amphora in process of subdivision. 
At the commencement of the phenomenon, by reason of the 
short distance the hoops are able to slide, and also on account of 
the limited space which exists between the parent valves, it 
frequently happens that the young frustules take a somewhat 
oblique position, and their shape seems to be more or less flattened 
on account of it. The effects of this compression gradually disap- 
pear, so that at the moment of liberation, the. new frustules have 
completely acquired the appearance of the parent valves. 
The valve of an Amphora does not differ essentially from that of 
a Navicula except in the extreme eccentricity (excentricité ex- 
tréme) of its raphe; which is easily understood if we imagine a 
sufficient unilateral displacement of the central line and its nodules - 
in this latter species, and an increase of its convexity necessary to 
bear this new line upon the exterior side or hoop of the frustule. 
The link between the Navicule and the Amphore is furnished 
by the Cymbellee (see fig. 50). 
Fig. 50. 
1. Section of a valve of Navicula. 
2. 9 ” ” Cymbella. 
3. ” 39. ea Amphora. 
The eccentricity of structure in the Amphoree differs essentially, 
by its nature, from that of the Nitzschia noticed in a previous paper, 
in that in this instance the two small flaps of the same frustule are 
in contact ; while with the Nitzschia a large flap is always found to 
lie contiguous to the small flap of the other valve. Moreover the 
absence of a carina, the presence of a raphe and nodules, as well 
as the nature of the endochrome, set the genera Amphora and 
Nitzschia far apart from each other in all methods of natural 
classification. 
The inner structure of the valves in the case of the Amphoree, 
differs according to the species; from the delicate membrane 
which scarcely resists treatment even with diluted acids, to forms - 
presenting a degree of solidity which might be called polycistinic, 
frem their massive and crystalline aspect. The species of this 
