OF THE PROTOZOA. PERIDINI.EA. 273 



structure. This external tunic is decomposable, although it resists destruc- 

 tion much longer than tlie contained matters ; and it is esi3ecially after a 

 certain amount of change has proceeded, that its delicate retiform structure 

 is more distinctly exhibited. 



The figiu'e of Peridinicea is very various and bizarre : the simplest is that 

 of a spheroid divided into two segments, equal or unequal in size, by a trans- 

 verse ciliated fiuTOW or zone. In some instances one side is flatter and concave, 

 and, according to Perty, presents a wide opening, or elongated fissure (XXXI. 

 16), from which the filament may sometimes be seen to proceed. Moreover, 

 besides the transverse furrow, a second is seen in some species to proceed from 

 it at right angles, as far as the vertex of the anterior half, — as, for example, in 

 Dr. Allman's species Peridinium uberrimimi (XXXI. 16, 18), and in P. fuscum 

 and P. ocidatum {Glenodhiium cinctum, Ehr.). Indeed, in Glenodinium apicu- 

 latum Ehrenberg describes several subsidiary, shalloAver, hispid furrows branch- 

 ing over the surface (X. 224-226), and in G. tahidatum a series of non-hispid 

 lines or ridges. These last two forms recall in general features the pollen-cells 

 or grains of the higher plants, and may, indeed, from the deficiency of a loco- 

 motive filament, and from other exceptional characters, be considered doubtful 

 members of the family Peridinicm. An inequality of the two segments, as 

 separated by the ciliary zone, is seen in Peridinium Corpuscidum and P. mo- 

 nadicum, and in a less degree in P. ocidatum {Glenodinium cinctum). The 

 figure, however, is very curiously and materially altered by the production of 

 tapering or horn-like processes, of a large diameter and great length relatively 

 to the principal portion or body of the organism. These processes difter in 

 number in diiferent species, and give rise to very bizarre forms, dej^arting 

 widely from those of any Phytozoa or from any other ciliated Protozoa. The 

 number of horns in Ceratium Fusus is two, and, being in the same line, produce 

 the spindle-shaped figure of the entii^e being (X. 222, 223). In C. furca 

 two occur in front and one of larger dimensions beliind ; the same is seen in 

 P. Tripos (X. 219, 220), in which, however, the two anterior processes are 

 curved, — whilst P. cornutum {Ceratium HirundineUa) has from two to three 

 posteriorly, and one, usually curved, anteriorly. In Ceratium Micliaelis (X. 

 221), again, we see three short processes project from the posterior half ; and, 

 lastly, in C. macroceras (Perty) three are represented behind, of which the 

 central is much the longest and straightest, and in front one still longer but 

 rather curved. The length of the horns compared with the body of the Ce- 

 ratia affords, however, no specific character, inasmuch as it varies according 

 to age and probably also other conditions. The vibratile cilia are usually con- 

 fined to the groove surrounding the lorica, and to the direct continuations 

 from it. Nevertheless Dr. AUman discovers in P. uberrimum the whole sur- 

 face sparsely covered with them ; and Ehrenberg mentions the supplementaiy 

 farrows of Glenodinium apiculatum as occupied with hispid hairs (X. 224- 

 226). The locomotive filament, which Ehrenberg failed in seeing in all even 

 of his genus Peridinium, is usually of great length and tenuity, and, accord- 

 ing to the great Berlin micrographer, proceeds from the neigh boiu-hood of the 

 mouth which he believed he detected in Peridinium Fusus in a hollow near 

 the middle of the animalcule. Allman more definitely points out its situation 

 as being near the junction of the transverse and vertical furrows in the species 

 he has described (XXXI. 16). Lastly, Perty states that Ceratium HirundineUa 

 {C. cornutum, Ehr.), when swimming, stretches out the filament as if stifi", and 

 that, although 2^ times longer than the body, it may be easily overlooked, on 

 account of its active swinging movement. It is apparently a production of the 

 protoplasm, protmded externally through an apertiu'e in the investing tunics. 

 Opinion is divided respecting the existence of a mouth. Ehi-enberg repre- 



