356 GENERAL HISTORY OF THE INFFSORIA. 



tentacular processes at each end, siuTounded by small knobs, recalling in 

 figure the knobbed tentacles of some Acinetina (XXYIII. 14, XXIX. 30) ; 

 by means of these the embryo secures its hold to its parent. Such pro- 

 cesses are not present in all specimens, and are therefore non-essential ; or 

 it may be they have disappeared by withdi^awal into the general substance 

 of the body. 



The embryo once freed from its parent, commences an independent existence, 

 moving freely about in the water — much more similar in figure and structure, 

 however, to some of Ehrenberg's Ci/clidina or to Dujardin's Enchelyens than 

 to Parameciwn . Cohn notes its affinity with the Cyclidium margaritacenmy 

 or to the Pantotriclmm Enchelys (Ehr.), and also with several species of 

 Dujardin's genus Enchelys (Cyclidmm Ehr.). 



Cohn adds that, in his opinion, several embryos are developed simultaneously, 

 and that, where only one or two are found, others have already escaped. In 

 some instances he has noticed as many as six or eight in process of develop- 

 ment, and, it would seem, in almost precisely the same stage, although their 

 birth is successive. Fiu-ther, besides these normal embryos, he has fre- 

 quently witnessed the escape of others having a globular figure, clothed with 

 cilia and fm^nished with tentacular processes and a contractile vesicle. 



During the act of birth, the pulsations of the contractile space of the 

 parent are uninterrupted, and the rotation of the contents is arrested until 

 every germ has escaped. Another ciuious fact is, that the birth of embryos 

 may proceed as usual even whilst the act of fission is taking place in the 

 parent animal. 



The further history of the free embryo is not known ; yet, in aU pro- 

 bability, it is ultimately transformed into a perfect Paramecium, — an event 

 which, from its figui'e and stnicture, ensues readily and perhaps without more 

 than one intermediate phase. 



Judging from the above details, it is probable, as before remarked, that the 

 development of embryos in Stentor cceruleus (XXIX. 8) recorded by Eckhard 

 {supra, p. 354) was a precisely similar phenomenon to that just described in 

 Paramecium ; and it is clear that the like obtains in Stentor polymorjjhus, in 

 an Opalina or Bursaria noticed by Siebold (probably the Bursaria Entozoon 

 Ehr., parasitic in a frog), in Urostyla grandis, as mentioned by Cohn, and in the 

 animalcule which we conceived to be Trichodina pedicuJus {A. N. H. 1849, 

 iii. p. 269). 



Since this was written, the indefatigable labours of Cohn have added, 

 another instance of this endogenous mode of development, in Nassula 

 elegans {Zeitschr. 1857, p. 143; XXYIII. 11-14). This animalcule possesses 

 an elliptic nucleus, having its nucleolus lodged in a fossa near one end, and 

 surrounded by a vesicle, just as in the Paramecium Bursaria. Among 

 many specimens, Cohn found several having a large, elliptic, hollow space, 

 evidently limited by a membranous wall. Where this space approached 

 nearest the external surface of the animalcule, this was depressed in a cup- 

 like foiTQ, and from its centre a canal or fissure (XXYIII. 11 /) penetrated 

 the interior of the space, where were two, never more, large globules, pj-jj'" 

 in diameter (XXYIII. 11 d). After a longer or shorter delay, these globules 

 escaped and appeared motionless, without coloui', but granular, and having a 

 central nucleus and an excentric contractile vesicle. As in the instance of the 

 germs of Paramecium Bursaria, no cilia, but a few short, knobbed, radiating, 

 tentacular-looking processes (XXYIII. 14), were visible on the siuface. Lastly, 

 Cohn noticed the formation of these germs in animalcules recently produced 

 by self-fission, and which had attained only one-half their normal dimensions. 

 The development of an embryo within an encysted animalcule is illustrated 



