774 LECTURE XLIII. 



' After what has been said above there can be little doubt that it is 

 actually this slime which acts specifically on the antherozoids. However I was 

 able to convince myself still more definitely of this action by moving the 

 cover-slip and thus bringing the slime out of its original place, or even removing 

 it entirely by means of the needle. The antherozoids then, held by the slime wher- 

 ever it came to lie, strove to free themselves from it or perished in it after a longer 

 or shorter swarming, but they were no longer directed towards the opening of 

 the archegonium-neck. 



'We will follow yet further the behaviour of the antherozoids inside the 

 central cell. Pteris is, as already seen, unfavourable for this observation, so that 

 among the numberless observed cases I was only able to see this process twice here. 

 Once on a transverse section which laid bare the archegonium, without injuring 

 it, and antherozoids from a neighbouring antheridium crowded into it; another 

 time on a superficial view of the prothallium, where the archegonium on the 

 declivity of the central cell-cushion came to lie so that I could see its optical 

 transverse section. 



' The whole process may be followed comparatively easily however in Cera- 

 topteris thalidr aides. The prothallium is so translucent that it is very easy on surface 

 views to see both the whole central cell and its contents, the tendency of the 

 archegonia to be placed at the inturned margins of the prothallus being still 

 more favourable for observation. The antherozoids are relatively larger than in 

 Pteris, and thus can be easily followed. 



' The first antherozoid which penetrates into the central cell abuts, generally 

 at once, or it may be after a short swarming, with its anterior end on the pale 

 spot (the receptive spot) seen about the centre of the top of the oosphere, and 

 at once remains fixed at this spot ; it then revolves rapidly round its axis and 

 its apex sinks slowly into the oosphere. Its movements become slower, and 

 sometimes cease entirely, it disappears more and more into the oosphere, and its 

 mass fades in it, till after 3-4 minutes (in all cases) nothing more is to be 

 seen of it. This process, as I have just described it, I have succeeded in following 

 quite undisturbed only five times out of the many cases observed, that is when 

 only one antherozoid had penetrated into the central cell; and this occurred 

 mostly only when access to the canal was impeded by means of external dis- 

 turbing influences, e.g. when air-bubbles or other foreign bodies blocked the 

 entrance to it. In most cases several other antherozoids follow the first 

 one, which thus becomes displaced by the new comers, unless it has 

 penetrated already with its apex to a certain depth. The antherozoids now 

 move in and out, and it is very difiicult to follow the individuals. Often two 

 or even three antherozoids are found simultaneously hanging by their apices 

 at the receptive spot: they rotate rapidly on their axes, mutually crowding, till 

 one obtains the upper hand, and is so far absorbed that its posterior coils 

 cover the receptive spot. The remaining antherozoids are then never retained 

 longer and swarm in and out for some time. Often their movements cease for a 

 time, to be resumed again after a few moments; this continues for 8-10 miniites, 

 and then all come to rest; and each individual antherozoid remains at the spot 

 where it came to rest and is here visible for some time longer. In one case 



