8 2 8 



THE ANIMAL KINGDOM. 



tion of a depression which widens at its inner end, but remains per- 

 manently open. It is open also in Trichophrya, but in Dendrocometes its 

 aperture closes. The closed brood cavities of other Acinetaria may be 

 formed in a similar manner, but the fact has not been observed. The bud 

 is produced as a process of the floor of the depression or cavity. When it 

 is single, as is commonly the case, it is of large size relative to its parent ; 

 when there are several buds, e. g. four in Acineta fetida, they are smaller, 

 and a difference of size has been noted in various instances, dependent 

 probably on the number formed 1 . The nucleus of the bud, whether 

 external or internal, has been seen to originate by fission of the parental 

 nucleus. It is beyond doubt always so formed. The bud or embryo, as 

 it is sometimes called, is ciliated, in some instances uniformly, sometimes 

 on one aspect only, e. g. Hemiophrya, sometimes in a zone, e. g. Podo- 

 phrya quadripartite Dendrocometes, Dendrosoma, and then the cilia appear 

 to be disposed not infrequently in a spiral. The passage of the em- 

 bryo into the parent form has been traced in several instances. That of 

 Dendrosoma, which is sessile, develops suctorial tentacles over the whole 

 free surface before a vertical stem begins to grow out 2 . 



Conjugation has been observed in some instances ; it may be tem- 

 porary, as in Dendrocometes, or permanent 3 . In Podophrya pyrum a forma- 

 tion of internal buds has been recorded as taking place immediately after 

 it. Encystation under unfavourable circumstances is frequent, the Acine- 

 tarian retracting its tentacles ; binary fission of the contents of the cyst 

 has been seen. 



The Acinetaria are microscopic in size. The colony of Dendrosoma 



1 See Claparede and Lachmann, Etudes sur les Infusoires, etc. ii. 1860-1, in Podophrya 

 pyrum, p. 123; P. quadripartita, p. 120-1 ; in Acineta fetida, Maupas, A. Z. Expt. ix. p. 320-1. 

 Embryoes contained within pocket-like diverticula of the cuticle at the aperture of the lorica have 

 been observed in Acineta tuberosa by Hertwig, M. J. i. p. 68, note I, and in A. mystacina, cf. Saville 

 Kent, Manual of the Infusoria, ii. p. 834. Hertwig suggests (loc. cit.) that they are due to a pre- 

 cocious fission of an endogenously-formed embryo, and states that the nucleus of the bud in Hemi- 

 ophrya gemmipara may commence to branch, the first indication of budding, before the bud itself is 

 detached. According to Saville Kent (op. cit. p. 844) external diverticula containing each an 

 embryo are found singly or in groups near the apices of the stems in Dendrosoma. He never saw 

 these buds become ciliate, but observed them with suctorial tentacles. Fraipont has given an account 

 of the formation of external capsules, ' diverticules generateurs,' in Acineta divisa. They are 

 pyriform, curved, with a terminal orifice : the protoplasm within them appears to be a process of the 

 periphery of the body. It gives origin to an ovoid bud with a zone (?) of cilia. The process of 

 protoplasm may give origin to a second, or to a series of such buds. See Bull. Acad. Roy. Belg. 44. 

 1877, p. 805. 



2 Whether spores are ever formed or not is an open question. Fraipont observed an encysted 

 Podophrya (= Hemiophrya} truncata resolved into minute spheres (op. cit. ante, 45, 1878, p. 296), 

 and Claparede and Lachmann state that Urnula Epistylidis gives rise to them (op. cit. ante, p. 210), 

 but they suggest also that the spores belong to a Chytridium (op. cit. p. 255, note). 



3 In Dendrocometes a bridge of protoplasm is formed : currents pass from one individual to the 

 other, and the nuclei are subsequently broken up and regenerated (Plate). Conjugation might be 

 mistaken for fission : see note 2, p. 827 ante. 



