ON SAPEOLEGNI^. 281 



commonly secondary and tertiary. Since the thallus has accu- 

 mulated much material, and the asexual reproductive organs 

 have been for tlie most part emptied when the oogonia arise, 

 it is usual to find empty zoosporangia terminating the main 

 twigs. The production of lateral branches from beneath the 

 sporangia is characteristic of Achlya, and that such may bear 

 oogonia is sufficiently demonstrated by fig. 9 b. Such is the 

 typical mode of development of the oogonium. Before pro- 

 ceeding to describe the changes which its contents undergo, 

 we may examine the mode of origin and growth of the so-called 

 " antheridial'' branches. 



These are longslender tubes, springing from the main branches 

 from points either close to the oogonia (fig. 10) or at greater 

 distances apart, or even from separate branches. The diameter 

 of the lube is commonly less than that of the pedicel, but may 

 equal it : within its thin walls are finely granular, watery pro- 

 toplasmic contents, not always easily distinguished. As seen 

 in fig. 12, the " antheridial branch" arises as a simple 

 tube ; it often begins to form branches soon after its origin, 

 and these spread in all directions, curling and waving as they 

 do so. In this manner they become wrapped or coiled around 

 objects, such as neighbouring branches or oogonia, with 

 which they come in contiict (fig. 9 b). It is in this coiHng 

 of the antheridium branch about an oogonium that the 

 first stage of a proper sexual process has been recognised by 

 earlier observers. 



During the development of the coiling antheridial tubes 

 above described, the granular, yellowish-grey contents of the 

 oogonium, undergo certain changes, which result in their 

 complete transformation into the egg-cells or oospheres. A 

 clear, almost watery spot appears in the centre of the mass 

 (fig. 11 a), and slowly increase in bulk as the dense grey 

 granular protoplasm recedes to the walls ; in this latter are 

 large, fatty-looking granules, which seen from the surface 

 (fig. 11 Z*) are in slow but evident motion. This retirement 

 of the protoplasm to the sides is followed by another process ; 

 a collection of the whole mass into two or more clumps, Avhicli 



