NOTICE OF THE GENUS TETRAPEDIA, ETC. 355 



cisions, a growth or increase of dimensions, so far as we can 

 judge, seems to occur, and each of the four quadrate sections, 

 when the incisions have progressed to this extent, appears to 

 be about equal in size to the original single quadrate cell. 

 The line of incision does not appear to be simply rectilineal 

 and acute below, but it leaves a somewhat considerable 

 interval betAveen the segments, and at the lower or inner 

 extremity it is. bluntly rounded, and higher up it offers a 

 somewhat undulate aj^pearance, whilst the general or average 

 breadth of the incision is pretty much alike throughout. 

 This undulate outline is due to the circumstance that each of 

 the four margins of the four segments, the two inner of each, 

 as well as the two outer, at this stage possesses a minute 

 emargination at the centre, the two new angles (or those at 

 the top or outer extremity of the incisions) being rounded off 

 similarly to the single old angle of each (or those forming the 

 four angles of the primary quadrate cell). As in a single 

 cell, the intervals between the central emarginations and the 

 angles offer a slight marginal concavity ; the remaining 

 angles of each of the four segments are, of course, those by 

 which they remain mutually connected. In fact, we have 

 now presented a cell with four quadrate segments, mutually 

 bonded together by the inner angles, the whole as yet forming 

 but one common cavity, each of these four segments, except 

 as to their being so united by one of their angles, offering all . 

 the same characteristics as the original single quadrate cell 

 (fig. 4). A further degree of complexity seems now to arise. 

 Taking origin from each of the emarginations at the centre 

 of each of the sides of all the four quadrate segments, into 

 which the original cell has become subdivided (as well from 

 those bounded by the lines of incision as those external), a 

 secondary incision takes place, proceeding likewise in a 

 direction perpendicular to the sides, and progressing until 

 each of these two almost reaches the centre. Like the 

 incisions of the primary cell, they also are somewhat Avide, 

 rounded beloAV, and with a somewhat undulate outline, due 

 to precisely the same circumstance, that at the middle of all 

 the sides of each and every of the new quadrate segments 

 (the inner as well as outer) a minute emargination presents 

 itself, and the angles being rounded, with a slight concavity 

 between these and the central emargination. Pari passu Avith 

 the formation of these further incisions of each of the noAv 

 ncAv quadrate segments of the segments of the original quad- 

 rate cell, they, too, in their turn become increased in size, so 

 as to equal their predecessors, as these equalled the original 

 cell, Avhilst they, likeAvise, remain bonded together by the 



