28 T. H. BUFFHAM ON CONJUGATION OF ORTHONEIS BINOTATA. 



known as the " front view " of the frnstule) it appears as a 

 half or three-fourths of a sphere, its base resting on the host 

 (Fig. 10). When seen from a point vertical to the base the 

 gelatinous investment has an elliptical outline of similar pro- 

 portions to that of the frustule. But from the extremities of 

 the minor axis there are mammiform protuberances through 

 which pass long processes of the same substance : these we 

 might call tentaculoids (Fig. 9)„ And to avoid circumlocution 

 I venture to propose for the gelatinous investment of this and 

 some other diatoms the term perigloea. 



The frustules vary in size from 42 by 30 /x to 23 by 18 fx. The 

 perigloea exceeds the dimensions of the frustule by about half in 

 length and breadth. Each tentaculoid, however, sometimes 

 reaches a length of 320 /jl ('0126 inch) while the diameter near 

 the mammiform part surrounding its base is 6 fx, and near its 

 apex 2 fi. Moreover their origin can be traced to those parts of 

 the frustule where the plates above described lie in apposition 

 (Figs. 9, 10). 



With regard to the ordinary mode of multiplication by divi- 

 sion of the frustule when the stage shown in Fig. 10 is reached 

 I am inclined to the view that both frustules are discharged 

 from the perigloea, for this is so uniformly perfect in outline 

 that no signs of a rupture are visible, although, on the other 

 hand, it is rare to see a valve completely free from any perigloea. 

 A very early stage is drawn in Fig. 7. Later on the swellings 

 through which the tentaculoids are projected are prominent 

 while the tentaculoids themselves are as yet only short and thin 

 (Fig. 8). 



We now come to the mode of conjugation. As in other 

 diatoms only the smallest individuals are concerned in this 

 process. A frustule which has completed, or almost reached, the 

 stage of self-division (as in Fig. 10), and is only 23 /x long, has 

 a bulbous addition to the upper part of its perigloea, into which 

 the double frustule rises. This speedily enlarges into a perfectly 

 spherical sporangium of 75 /x diam. The frustules occupy 

 the centre of this, and then the lower one imparts its 

 endochrome to the upper one. This upper frustule then 

 divides and forms two masses of endochrome which develop 

 into two sporangial frustules of exactly double the length and 

 width of the parent. One valve of the mother-f rustule is closely 



