APHANIZOMENON FLOS-AQUtE. 25 



a quiescent state, most likely preparatory to undergoing some 

 important developmental change, the contents contract towards 

 the centre, and then an external transparent and perfectly- 

 colourless vesicle becomes visible while the flagellum and cilia 

 disajipear, fig. 11. The contracted contents present a very 

 definite and generally spherical boundary, and are evidently 

 included in a distinct cell : the resemblance of this internal 

 cell to the primordial utricle, and that of the external investing 

 vesicle to the cellulose wall of the vegetable cell, are too 

 obvious to be overlooked, though the iodine and sulphuric 

 acid test failed in indicating the presence of cellulose. The 

 external investing vesicle is non-contractile ; under pressure it 

 is easily ruptured, and the minutely-granular contents, mixed 

 with large oil-drops (?), escape upon tlie stage of the micro- 

 scope, fig. 12. The nucleus is then easily isolated ; it is of an 

 irregular, oval form, quite colourless, and marked on its surface 

 with curved stria?, fig. 13. 



Individuals were frequently seen undergoing spontaneous 

 division, which takes place parallel to the annular furrow, and 

 in the unfurrowed hemisphere, fig. 14. This process appeals 

 to be invariably preceded by a division of the nucleus, and 

 the author had succeeded in isolating nuclei, presenting almost 

 every stage of transverse fission, figs. 16, 17. 



Believing the species now described to be new, I have 

 named it P. uberrima. 



Since communicating the above facts to the Academy, the 

 coloration of the ponds has much increased in intensity. 

 On the 9th of July I again visited them. The colour in 

 some parts was then of so deep a brown, that a white disc, 

 half an inch in diameter, became invisible when plunged to 

 a depth of from 3 to 6 inches, while a copious exit stream, 

 which constantly flowed away from one of the ponds, pre- 

 sented the same deep-brown tint. In many places the 

 Peridinea had descended from the surface, and were found to 

 be congregated in immense masses towards the bottom, where 

 they appeared to be quite healthy, though presenting the con- 

 dition described above as characterising the quiescent state of 

 the animalcule. It is highly probable that this contracted 

 condition of Peridinea — a condition, however, which must not 

 be confounded with the encysting process observed in many 

 infusoria — is connected with reproduction. A field of much 

 interest is here open for investigation, but I was unfor- 

 tunately at this point obliged to discontinue my observ- 

 ations. 



