MAST1GOPHORA : CYSTOFLAGELLATA. 853 



are various ; it may be retracted and shot out, lashed about, traversed by 

 short rapid, or long and slow undulations. It appears to have periods of 

 quiescence. 



Noctiluca passes into a resting condition but forms no cyst. The 

 tentacle is absorbed, the mouth closed, the peristome, &c. obliterated, but 

 the central mass of protoplasm persists. How the organs in question are 

 regenerated is not known to a certainty 1 . Reproduction is by fission and 

 gemmation. It is possible that the former may occur in an ordinary 

 individual, but as a rule the tentacle is thrown off, and all the organs with 

 the exception of the mouth obliterated. The animal becomes elongated 

 transversely, the nucleus first divides with mitosis, then the central mass 

 of protoplasm, and finally a median furrow cuts the two halves asunder. 

 A new tentacle begins to bud out before separation is complete ; the peri- 

 stome and other organs are also reconstituted. Gemmation is often, per- 

 haps always, preceded by conjugation, which takes place by the fusion of 

 two ordinary or resting individuals. The two always come into contact by 

 the peristome or the spot where the peristome lay. The tentacles of the 

 ordinary individuals are said to be thrown off. In gemmation the central 

 mass of protoplasm forms a superficial projection, the nucleus divides, and 

 then the projection ; and by continuous binary fission, carried out in the 

 same way, a number of spores, amounting to 256 or more generally 512 

 (circa), take origin. The branching cords of protoplasm are retracted 

 during the process, and the nuclei enter the dividing projections as soon 

 as they number 64. The ripe spore is attached to the parent by a slender 

 pedicle and it developes a flagellum before detachment. It is -076 -020 mm. 

 in length, and viewed laterally has the shape of a coffee bean with one 

 end, the anterior, broad, and the other, or posterior, pointed, with one 

 aspect, the dorsal, convex, and the other, or ventral, slightly concave. The 

 concavity is bordered on each side by a ridge, the two ridges meeting 

 posteriorly (= staff-organ?). Its anterior end is crossed by a furrow from 

 which springs the flagellum, and, according to Cienkowski, a thick rod-like 

 process ( = tentacle ?). The flagellum is 6-7 times the length of the body, 

 and is an organ of locomotion. There is a bean-shaped nucleus, and a 

 slowly contractile vacuole (Robin) ; the protoplasm is homogeneous. The 

 further development of the free spore is not known. It probably passes 

 into the adult by direct growth 2 . 



Noctiluca is a voracious animal and floats on the surface of the sea. 

 It is phosphorescent when the water is disturbed, and it appears to emit 



1 The Pyrocystis pseudonoctiluca of Wyville Thomson and Murray, is probably a resting 

 Noctiluca ; and P. fusiformis a similar condition of an unknown Cystoflagellate. See Butschli, 

 Protozoa, pp. 1061-2, and Wyville Thomson and Murray, P. R. S. xxiv. 1876, p. 533, PI. 21. 



2 Cienkowski describes some abnormal forms of attached spores which favour this supposition ; 

 see A. M. A. ix. p. 56. 



