MICROSCOPIC FORMS OF ANIMAL LIFE. 37 



ity for several seconds, and then gradually disappearing. He was thus 

 able to satisfy himself that the special seat of the phosphorescence is the 

 peripheral protoplasmic reticulation which lines the external structureless 

 membrane. 



431. The reproduction in this interesting type is effected in various 

 ways. According to Cienkowsky, even a small portion of the protoplasm 

 of a mutilated Noctiluca will (as among Rhizopods) reproduce the entire 

 animal. Multiplication by fission or binary sub-division, beginning in 

 the enlargement, constriction, and separation of the two halves of the 

 nucleus, has been frequently observed. Another form of non-sexual repro- 

 duction, which seems parallel to the ( swarming ' of many Protophytes, 

 commences by a kind of encysting process. The tentacle and flagellum 

 disappear, and the mouth gradually narrows, and at last closes up ; the 

 meridional groove also disappears, so that the animal becomes a closed 

 hollow sphere. The nucleus elongates, and becomes transversely con- 

 stricted, and its two halves separate, each remaining connected with a 

 portion of the protoplasmic network. This duplicative subdivision is 

 repeated over and over again, until as many as 512 ( gemmules ' are formed, 

 each consisting of a nuclear particle enveloped by a protoplasmic layer, 

 and each haying its flagellum. The entire aggregate forms a disk-like 

 mass projecting from the surface of the sphere; and this mass sometimes 

 detaches itself as a whole, subsequently breaking up into individuals ; 

 whilst, more commonly, the gemmules detach themselves one by one, the 

 separation beginning at the margin of the disk, and proceeding towards 

 its centre. The gemmules are at first closed monadiform spheres, each 

 having a nucleus, contractile vesicle, and flagellum; the mouth is subse- 

 quently formed, and the tentacle and permanent flagellum afterwards 

 make their appearance. A process of 'conjugation* has also been ob- 

 served alike in ordinary Noctilucce and in their closed or encysted forms, 

 which seems to be sexual in its nature. Two individuals, applying their 

 oral surfaces to each other, adhere closely together, and their nuclei be- 

 come connected by a bridge of protoplasmic substance. The tentacles 

 are thrown off, the two bodies gradually coalesce, and the two nuclei fuse 

 into one. The whole process occupies about five or six hours, but its re- 

 sults have not been followed out. 1 



432. Intermediate between the proper flagellate, and the true ciliate 

 Infusoria, is the small group of CiUo-flageilata, in which, while the body 

 is furnished with rows of cilia, a flagellum is also present. Although 

 this group does not contain any great diversity of forms, yet it is specially 

 worthy of notice, on account of the occasional appearance of some of 

 them in extraordinary multitudes. This is the case, for example, with 

 the Peridinium observed by Prof. AJlman, in 1854, to be imparting a 

 brown color to the water of some of the large ponds in Phoenix Park, 

 Dublin; this color being sometimes uniformly diffused, and sometimes 

 showing itself more deeply in dense clouds, varying in extent from a few 

 square yards to upwards of a hundred. The animal (Fig. 300, A, B) 

 has a form approaching the spherical, with a diameter of from 1-1 000th 

 to l-5000th of an inch; and is partially divided into two hemispheres, by 



1 Noctiluca 

 are the most recent: 

 and Bd. ix. (1873), p. 



p. 327; Robin, "Journ. de 1'Anat. et de Physiol.," Tom. xiv. (1878), p. 586'; and 

 Vignal, "Arch, de Physiol.," Ser. 2, Tom. v. (1878), p. 415. 



