Sub-Order 2. =Coccochromaticæ.= The chromatophores are granular, small and many in each cell. The structure of the cells is zygomorphic or centric, often with reticulate markings. The following groups belong to this sub-order: _Fragilarieæ_, _Meridieæ_, _Tabellarieæ_, _Licmophoreæ_, _Biddulphieæ_, _Anguliferæ_, _Eupodisceæ_, _Coscinodisceæ_, and _Melosireæ_. Class 4. =Schizophyta, Fission-Algæ.= The individuals are 1--many celled; the thallus consists in many of a single cell, in others of chains of cells, the cells dividing in only one definite direction (Figs. 18, 21). In certain Fission-Algæ the cell-chain branches (Fig. 30) and a difference between the anterior and the posterior ends of the chain is marked; in some, the cells may be united into the form of flat plates by the cell-division taking place in two directions; and in others into somewhat cubical masses, or rounded lumps of a less decided form, by the divisions taking place in three directions; or less defined masses may be formed by the divisions taking place in all possible directions. The cell-walls rarely contain cellulose, they often swell considerably (Figs. 20, 22), and show distinct stratifications, or they are almost completely changed into a mucilaginous mass in which the protoplasts are embedded, _e.g._ in _Nostoc_ (Fig. 22), and in the “Zooglœa” stage of the Bacteria (Fig. 27). Sexual reproduction is wanting. Vegetative reproduction by division and the separation of the divisional products by the splitting of the cell-wall or its becoming mucilaginous; among the Nostocaceæ, Lyngbyaceæ, Scytonemaceæ, etc., “Hormogonia” are found; in _Chamæsiphon_ and others single reproductive akinetes are formed. Many Fission-Algæ conclude the growing period by the formation of resting akinetes or aplanospores. The Schizophyta may be divided into 2 families: 1. SCHIZOPHYCEÆ. 2. BACTERIA. Family 1. =Schizophyceæ,[5] Blue-Green Algæ.= All the Blue-green Algæ are able to assimilate carbon by means of a colouring material containing chlorophyll (cyanophyll); but the chlorophyll in this substance is masked by a blue (phycocyan), or red (phycoerythrin, _e.g._ in _Trichodesmium erythræum_ in the Red Sea) colouring matter which may be extracted from them in cold water after death. The colouring matter, in most of them, permeates the whole of the protoplasm (excepting the cell-nucleus), but in a few (_e.g._ _Glaucocystis_, _Phragmonema_), slightly developed chromatophores are to be found. Where the cells are united into filaments (cell-chains) a differentiation into apex and base (_Rivulariaceæ_) may take place, and also between ordinary vegetative cells and heterocysts; these latter cannot divide, and are distinguished from the ordinary vegetative cells (Fig. 22 _h_) by their larger size, yellow colour, and poverty of contents. Branching sometimes occurs and is either true or spurious.