186 
V. II. Blackman. 
of the cellulose wall is difficult to understand ; of its existence 
there can be no doubt, it is always very obvious, both from its 
general appearance and its reactions. 
The absence of flagella, the presence of yellow-brown chromato- 
phores and of a continuous cellulose wall, are all characters 
which separate it from Noctiluca ; there seems little doubt that, 
had Biitschli recognised the wall, he would not have connected 
Py rocystis with that organism. The striking difference of distribution 
of these two organisms would almost alone negative any idea of 
their relationship. They are never found together, Pyrocystis being 
nearly always pelagic, while Noctiluca is nearly always coastal. 
The only points of similarity are their arrangement of protoplasm 
and their luminous power. The depression in the protoplasmic 
substance of P. pseudonoctiluca shown in Murray’s figure is not a 
normal condition (it may be the first indication of division of the 
cell), and cannot be compared, as Biitschli supposes, to the peristome 
depression of Noctiluca. In face of this evidence the view 
that Pyrocystis noctiluca is a stage in the life history of Noctiluca 
must be abandoned. 
Granting, however, the vegetable affinities of Pyrocystis, there 
is still great doubt as to its systematic position, owing to our 
ignorance of the life-history of the various forms. 
Schtitt (8), an account of the resemblances of Pyrocystis 
with certain encysted states of Peridinere, would place them near 
that group. He admits, however, that they have certain resem¬ 
blances to the simple Desmids, though they differ in the arrangement 
of their protoplasm, and in the form and colour of their 
chromatophores. 
Haeckel (4) places Pyrocystis in the group Murracytese 
(Pyrocystales), in the Paulotomece division of the Algte. He thinks 
that they are probably a group of very simple structure and of 
great antiquity. Believing erroneously that the wall contained 
silica, he suggests that they may have given origin to the Diatoms. 
Schiitt (9, 10) figures, as mentioned earlier, the development of 
Gymnodiniuni- like flagellate spores with a horizontal furrow, in the 
cell of Pyrocystis lunula and on that account places the Pyrocysteae 
with Gymnodiniuni in the Gymnodiniacem, a division of the Peri- 
diniales. As Schiitt’s figures are published without comment or 
discussion, criticism is a matter of some difficulty, but it must be 
pointed out that no trace of a flagellate stage has been observed in 
any of the other four species of Pyrocystis (in spite of the great 
