OBSERVATIONS ON THE GENUS PYTHIOM. 5J3 



and, after what was said before, need not be further dwelt 

 upon. 



The development of the zoospores may be more fully de- 

 scribed, since it affords further distinctions for separating 

 this species. At 10 o'clock a.m. the ovoid zoosporangium 

 was fully formed, and had developed its short vertical beak 

 from the distal extremity or apex (fig. 41, a). It remained 

 almost unchanged during an hour, the only recognisable changes 

 being the movements of the numerous minute granules, and 

 the formation of ten or twelve small vacuoles (fig. 42, 2) in 

 the protoplasm. These soon disappeared, and the end of the 

 beak became more transparent and its walls marked by fine 

 longitudinal striae. At 11.40 a.m. the granular contents passed 

 out slowly, inflating the substance of the beak into a delicate 

 gelatinous vesicle in the mode already described in P. proli- 

 ferum. Here, also, the mass commenced to divide into 

 zoospores, passing through similar stages, and finally be- 

 coming free (figs. 41, b-d). All these processes occupied a 

 perceptibly longer time ; in this case, however, nearly twenty 

 minutes having elapsed between the emission of the protoplasm 

 and the completion of the zoospores within the vesicle. At 

 12 o'clock the young zoospores were moving independently 

 (d), tumbling one over the other with active amoeboid move- 

 ments, and soon afterwards the cilia appeared, at first short and 

 slowly waving, then soon elongated, apparently at the expense 

 of the knobs at their extremities, and by eight minutes past 

 12 the ten zoospores were rapidly flitting about. One minute 

 later (at 12.9) the vesicle gave way, and the free zoospores 

 escaped in the usual manner. 



The gemination of the zoospore took place in the usual 

 manner (fig. 43, a) after the swarming, and in one case I 

 observed the entry through the cuticle of a dead cress-seedling 

 (fig. 43, b). But the process of zoospore-formation may 

 occupy even a longer period than above described. In the 

 specimen drawn at fig. 42 (4-6), the separated zoospores 

 moved in an active amoeboid manner for more than an hour 

 before the cilia were developed. Of course, that this Py thium 



