XXll PROCEEDINGS OF THE 



parenchyma- cells of higher animals. These two products of diffe- 

 rentiation are designated by Haeckel " exoplasm" and " endoplasm." 



The exoplasm is originally a perfectly homogeneous and structure- 

 less, colourless, hyaline layer, distinguishable from the turbid granular 

 soft protoplasm of the internal body-mass by containing in its com- 

 position less water, by absence of included granules, and by its high 

 independent contractility. All the mobile appendages of the body, 

 the cilia, bristles, spines, hairs, hooks, &c., are nothing but struc- 

 tureless extensions of this exoplasm, and participate in its contrac- 

 tility. In this respect they entirely correspond to the cilia and 

 flagella of the cells which form the ciliated epithelium of multi- 

 cellular animals. 



In many Ciliata we find this cortical layer or exoplasm itself sub- 

 sequently differentiated into distinct strata. In the most highly 

 differentiated Ciliata four layers may be distinguished as the result 

 of this secondary differentiation of the exoplasm. These are : — 

 1, the cuticle layer; 2, the ciha layer; 3, the myophan layer; 

 4, the trichocyst layer. 



The cuticle is nothing but a lifeless exudation from the surface. 

 In the majority of Ciliata there is no true cuticle, and in those which 

 possess it it presents itself under various forms, as seen in the thin, 

 chitine-like, hyaline, homogeneous pellicle of Paramecium and Tri- 

 chodina, the outer elastic layer of the stem of the Vorticellinse, the 

 protective sheath of Vaginicola, the chitine-like cases of the Tintin- 

 nodese and Codonellidae, the beautiful lattice-like siliceous shells of 

 the Dictyocystidse and many other shells, cases, and shield-like 

 protections*. 



* In the same niimber of the ' Zeitschrift ' Haeckel ("Ueber einige neue 

 pelagische Infusoi-ien ") clcBcribes some highly interesting Infusoria which spend 

 their lives in the open sea, and are distinguished by the possession of variously 

 formed shells. His attention was first directed to them by finding their elegant 

 empty shells in the extracapsular sarcode of Radiolaria. These pelagic Infu- 

 soria appear to belong to two different groups, which stand nearest to the Tin- 

 tinnodea of Claparede and Lachmann. He designates them as Bidyocystidm 

 and CodoncUida. 



The family of Dictyouystidse is based on Ehrenberg's Dictyocysta, and is cha- 

 racterized by the possession of a siliceous perforated lattice-like shell, so closely 

 resembling that of many Radiolaria, that Haeckel at first mistook it for the shell 

 of one of these. The shell is in all the species bell-shaped or helmet-shaped, 

 and the body of the animal, which is fixed to the fundus of the bell, and can 

 be projected far bc_)ond its margin, has a wide funnel-shaped peristome, on 

 whose edge are two concentric wreaths of strong cilia. He describes four species, 

 distinguishing them by characters derived from their siliceous latticed shell. 



