GENERAL CHARACTERS OP BRITISH LICHENS. 73 



cavity of the spermogone. From their apices or sides the 

 sterigmata generate the Spermatid, which are minute, aci- 

 cular or linear bodies, straight or curved, varying in length 

 and breadth, sometimes oval or ellipsoid, colourless, trans- 

 parent, and which sometimes exhibit Brownian movements, 

 but are destitute of cilia or other appendages. "When thrown 

 off from their parent cells, these bodies gradually accumulate 

 in the cavity of the spermogone to such an extent that, 

 when fall of spermatia, this organ becomes so dense that it 

 may frequently be picked out of the thallus by means of a 

 needle-point : they ultimately escape from the spermogone 

 by means of its apicial pore. These bodies may be regarded 

 functionally as the analogues of the antherozoids of the 

 Cham, seaweeds, and other higher cryptogamic plants, from 

 which however they differ remarkably in being developed on 

 the exterior, instead of in the interior, of the parent cells. 

 The spermatia are developed long prior to the spores ; and it 

 is most important that the student should bear this in mind, 

 as it is the key to the relation of these bodies to each other 

 in respect to function. He will therefore select for the study 

 of the spermogones and their contents young plants prior to 

 the development of their apothecia, and will carefully look 

 for them in the form of black point-like bodies, scattered, 



