9 THE PH.EOPHYCEAX ZOID 



under a covei'slip). *' Several houi*s " is the rule ; many swim all 

 day, but none have been checked longer than 24 hours (Yamanouchi, 

 for Zaiiardinia^ 1913). In open water there seems to be no reason 

 why zoids with several chloroplasts might not continue for much 

 longer periods. For the shorter motile phase of more decadent types 

 Sauv^ageau gives 4-5 minutes for the megazoid of Giffordia virescens^ 

 and 15 minutes for the microzoid. In other examples the *' megazoid," 

 only just tumbles out of the gametangium, or is discharged immo- 

 tile {Acinetospora) ; probably all transitions occur. 



From such data it would appear improbable that these zoids can 

 raise themselves from any great depth ; though they do so freely 

 enough in culture vessels, spreading out as a film on the surface 

 {Cutleria, Aqlaozonia). 



Monstrosities in zoid-segregation suggest further points of interest 

 as tending to throw light on the organization of other zoids. The 

 occurrence of ** twin "-zoids, apparently due to the imperfect separa- 

 tion of protoplast-primordia in the '* sporangium " is described for 

 Pylaiella fulvescens (Sauvageau) 2Lwdi Aglaozonia (Kuckuck). The 

 more aberrant case of a "triplet" zoid in Aglaozonia (Kuckuck, 

 1899, W. M. K, p. 103) with triangular arrangement of 3 clear 

 "anterior ends," and a single flagellum on two adjacent sides, is of 

 special interest from the standpoint of the suggested flagellated phase 

 of the Diatom Biddulphia mohiliensis (Bergop, 1907, Bull. Soc. 

 Bot. p. 348), in which a protoplast is figured with 3 " flagella " 

 at three angles. 



Several phyla of the Phteophycese are distinguished by distinct 

 variants on the type. In Phaeosporeae the zoid is typically ovoid, 

 with distinctly-pointed anterior end, and two flagella inserted laterally 

 near the pointed anterior end : the anterior (tractor) flagellum is 2-3 

 (or 4) body-lengths, and the trailer short (one body-length). Through- 

 out the Laminariaceae and Cutleriacese the same type prevails ; but 

 among the more advanced Fucoids of the Cys^os<?/r«-alliance the 

 antherozoid is more rounded, and often shows no pointed end at all ; 

 the anterior flagellum is still long (2-4 body-lengths). Among the 

 Fuceae, in the stricter sense, a more specialized zoid is characteristic, 

 with a slender bottle-shaped form and a sharp-pointed beak; the 

 anterior flagellum is now the shorter (11-2 body-lengths) with stout 

 basal portion, and the posterior as a long trailing steering-oar is 

 2|-3 body-lengths. Pelvefia has the shortest working-arm (1 length), 

 and the movements are more jerky than those of Fucus, the zoids of 

 which show a straight gliding movement. The pattern with the 

 boring tip is characteristic of the littoral forms {Fucus, Pelvetia, 

 Ascophyllum), and it would appear that the forms with more 

 advanced oogamy (Ct/stoseira, Himanthalia, Sargassuni) 2iYeieni\\x\g 

 to further decadence of the flagellated phase in the case of the micro- 

 gamete, as is certainly the case in the advanced series of the 

 ■ Dictyotaceae. 



It may be concluded that, evolved as a somatic organ in an active 

 plankton-phase, now reduced to a rejuvenated zoid, the flagella had 

 no original value for lateral progression ; but the inherited mechanism 

 on hand suffices to bring the protoplast into close contact with a 



