OF THE PROTOZOA. PEEIDINI^A. 275 



smaller size than usual, yellow in colour, and not, like older animalcules, 

 greenish-brown or brown, which had from 10 to 12 red vesicles or globules 

 about the middle of the anterior segment. Still the general rule is that in 

 very young indi\iduals no stigma is present. The inconstancy of the presence 

 of the red speck, even in matiu-e specimens, its absence in very young, its dis- 

 appearance in old ones, and the many irregularities, not only in its occurrence 

 but also in size and number, are facts which sufficiently prove its worthless- 

 ness as a generic or even as a specific distinction, and which declare against 

 its assumed function of a visual organ in this as in other families of Protozoa. 



REPEonrcTioN. — Longitudinal fission has been seen to take place in several 

 species. Self-di\T.sion, says Perty, presents many peculiarities among the 

 Pendinicea. In Ceratium HirimdineUa, fission is longitudinal ; it commences 

 anteriorly close to and on the left side of the great horn (as the animalcule 

 is viewed from above), and advances towards the posterior extremity. The pro- 

 cess is not confined to the large specimens, but is equally enjoyed by the small. 



During the act of fission in Peridinium Pidviscidus, Perty noticed that 

 before its completion the newly-formed segment continued to augment in 

 size until it surpassed the original being, which underwent no enlargement. 



Dr. Allman noticed, in the species he examined (J. M. S. 1854, p. 25), that 

 spontaneous division took place " parallel to the annular furrow " (XXXI. 

 18), i. e. therefore transversely, "■ and in the unfurrowed hemisphere." He 

 also remarked the important fact, that this process appears to be invariably 

 preceded by a di\T.sion of the nucleus ; and he had succeeded in isolating nuclei 

 presenting almost eveiy stage of transverse fission. But besides their reproduc- 

 tion by fission, Perty adopts Ehrenberg's \dews and insists on their development 

 from ova or ovules, which present themselves in the form of brown or green 

 corj3uscles in the interior. Peridinium tahulatum is often seen to be full of 

 such, elHptic in figure, and as much as 1-150'" in length, and which can be 

 expelled by pressure from the animalcule. In P. Pidviscuhs Perty met with 

 specimens from 1-400'" which were aggregated together in masses, and moved 

 together. In P. Oorpiiscidum, he asserts, development from ovules may be 

 directly observed ; and he gives figures of ovules set free, and of the young 

 generated from them, which would seem the same structures with the addition 

 of a cell- wall. The ovules, too, are large and very e\ddent in Ceratium cornutum ; 

 and he regards the small brown organisms which may be found in company with 

 mature individuals at various times of the year, as the primitive stage of ge- 

 neration of those ova before acquiring the perfect figure of Ceratium. In some 

 specimens, indeed, he remarked the long filament peculiar to the species, and a 

 red stigma in the posterior segment. The smallest examples measured 1-200'", 

 and were at first elliptic ; from this they changed to reniform, and became 

 distinguished into an anterior and a posterior half. Their movement was ro- 

 tatoiy or spiral, and quicker than in old individuals. On one occasion he saw 

 small examples of Ceratium Hirundinella only 1-25'", of the same figure as the 

 large specimens, but completely colourless ; at another time he encountered 

 pale brownish-green individuals, with a beautiful red stigma, and the poste- 

 rior lateral horns scarcely developed, — whilst in one instance the anterior 

 cornu was completely formed, and the posterior extremity rounded. These 

 examples, he observes, appear to be different structural phases through which 

 the products generated from the ovules have to pass. 



The reproduction by ovules or internal germs has its parallel in Euglencea ; 

 and, like as in this group, so in the family Peridinicea a quiescent, resting, or 

 " still '* stage appears to occur. Dr. Allman has put forward this fact most 

 clearly. He writes (,/. M. S. 1854, p. 24) — " Before death, and also when 

 passing from a motile to a quiescent state, most likely preparatory to under- 



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