GENUS NOCTILUCA. 399 



become separated by binary segmentation into at first two and then consecutively 

 four, eight, sixteen, thirty-two, or more masses in a manner corresponding precisely 

 with what has been previously described of many ordinary Flagellata. The cuticular 

 surface next becomes nodular to adapt itself to the contour of the subjacent segment- 

 masses, and these at length penetrating through the cuticle, remain attached for a 

 short while on its external surface, developing there a long flagelliform appendage, 

 and become ultimately detached as simple monadiform germs. The germs or 

 daughter-cells, thus developed, are usually aggregated in a discoidal or cake-like 

 form at one pole of the exterior surface, as shown at PI. I. Figs. 35 and 37, but 

 sometimes take a more loosely reticulate arrangement, Fig. 36, or may form an 

 equatorial girdle around the parent envelope. A considerable variety of contour is 

 exhibited by these germs. In their most typical aspect, PI. I. Figs. 39 and 40, they 

 are somewhat conical, with a rostrum-like process which apparently represents 

 the rudimentary condition of the subsequent rod-like induration of the cuticle are 

 divided by an annular groove into an anterior and posterior region, and have a 

 short, tongue-like appendage and a long, flexible, lash-like flagellum. In another 

 and probably earlier state the germ is a simple spheroidal sac with or without 

 the lash-like flagellum, Figs. 37 and 38. 



The conjugation of adult N'octilucce in either their normal or spheroidal state has 

 been frequently observed, and is manifested in the first instance by the close apposi- 

 tion of their respective oral surfaces. The tentaculiform appendages are then cast 

 off, the two endoplasts become united by a bridge of endoplasm, and the two bodies 

 gradually coalescing, Fig. 44, are within the space of five or six hours indissolubly 

 fused together. This process, though evidently requisite for the occasional rejuvena- 

 tion of the reproductive functions, is apparently not a necessary precedent to each 

 reproductive act. The recuperative properties possessed by this animalcule are 

 somewhat remarkable ; a crushed or otherwise mutilated zooid withdraws its flagel- 

 lum, and after contracting into an irregular protoplasmic mass, develops a fresh 

 cuticular investment, while the smallest portion of sarcode, separated from the 

 parent, is capable of growing into a perfect zooid. The food of Noctiluca consists 

 chiefly of the floating Diatomaceae which occur in such abundance upon the upper 

 stratum of the ocean, numerous varieties of which will frequently be found entangled 

 within the internal radiating protoplasmic network. Elaborate and masterly accounts 

 of the leading structural features of this highly interesting type, which have served as 

 a basis for the foregoing technical diagnosis, have been contributed by Professors 

 T. H. Huxley and G. J. Allman to the ' Journal of Microscopical Science ' for the 

 years 1855 and 1872. 



There can be but little doubt that the organism figured by Professor Sir Wyville 

 Thompson in the 'Proceedings of the Royal Society,' vol. xxiv., pi. 21, 1876, as 

 a new diatom under the title of Pyrocystis pseudonoctihica his illustration of the 

 same being reproduced at PI. I. Fig. 45 represents the normal encysted condition 

 of Noctiluca miliaris as previously described by numerous investigators, and notably 

 by Johannes Miiller, as translated in the 'Journal of Microscopical Science' for 

 1855. The account there given runs as follows : " These encysted bodies consti- 

 tuted the principal luminous animalcules observed at Messina in the autumn of 1853. 

 Free Noctiluccz at that season were not seen there; and in 1849 the same kind of 

 encysted bodies were very common at Nice. The cyst is a perfectly transparent, 

 spherical capsule, with a light-bluish brilliancy at the edge, and appearing like the 

 egg-membrane of some Crustacea. Within the cyst is lodged a body in all respects 

 resembling Noctiluca miliaris, except that at this time no vibratile filament can be 

 perceived. The Noctiluca-Vke. creature fills the cyst more or less entirely, though 

 occasionally it is much smaller. In this condition the animalcules are luminous 

 without being agitated." Professor Wyville Thompson's second species, distin- 

 guished by the title of Pyrocystis fusiformis (PI. I. Fig. 54), represents apparently a 

 similar quiescent phase of Leptodiscus medusoides, next described. It is a remark- 

 able circumstance, and one perhaps not altogether worthy of congratulation, that, 

 excepting for a passing notice of the occurrence of Peridiniiclae in certain latitudes, 

 the very existence even of the important and highly interesting organic group 



