4 THE PIIJEOPHTCEAN ZOID 



in the case of increasing mass or form-resistance in the body of the 

 protoplast, the vortical motion will become a means of impelling 

 food-particles on to the point of insertion of the tractor ; and in the 

 vast series of more dominantly holozoic flagellate organism this 

 becomes the essential mode of " feeding " ; such particles being 

 absorbed, ingested, and ultimately digested in an oral depression, 

 cytostome, or gullet, as the " animal " flagellate is more definitely 

 outlined (cf. ChiIomo7ias, Cyatliomonas, Gymnodiniaceae). No trace 

 of such holozoic nutrition has been observed in any zoid of the 

 Phceophyceae ; and the utilization of these as non-metabolizing re- 

 productive cells suggests that any such tendency will be further 

 eliminated in their short life-period (as the anterior tractor has been 

 apparently eliminated in Metazoan sperms). For ingestion by Green 

 Algal zoids cf. Pascher, Berichte xxxiii. p. 427. 



Secondary increase in volume obtains throughout the group in 

 several series independently, as heterogamy progresses (to define the 

 *' female " gamete), as also in the case of the correlated increase of 

 the asexual zoogonidia. In such case the zoid retains its general 

 attributes ; the chloroplasts may be greatly increased in number, and 

 the flagella keep pace to a certain extent ; in extreme cases, however, 

 the latter begin to dwindle ( Qiffordia virescens, Pylaiella ful- 

 vescens Sauvageau *, 1896), and may be apparently wholly lost 

 (^Aci7ietospora Bornetf), though euglenoid motility may be retained. 

 In the larger megagametes (** oospheres ") no trace of flagellation 

 remains, and the same applies to the correspondingly enlarged tetra- 

 spores of Dictyota and the *' monospore " of Haplospora. 



Interest also centres in the evidence of distinct reduction in the 

 case of the microgamete (antherozoid) in correlation with the 

 differentiation of heterogamy and the relegation of the zoid to the 

 mere value of a " sperm." Thus in Fucus serratus, according to 

 Eetzius (1906), the body of the zoid is practically restricted to an 

 oval nucleus, more or less flattened (Meves), to which the C3^toplasm 

 constitutes only a thin film, more exaggerated to form the anterior 

 pointed end. The residual '* ej'e-spot " and the " mitochondrial 

 a))paratus " of 4 granules (often merging into one, Meves), whether 

 of cj-^toplasmic nature or merely physodes (Kylin), so far project 

 from the surface of the plasma-film, and may be even stripped 

 off (Retzius, Biolog. Untersuch. 1906) %. The case of Dictyota 

 suggests the gradual elimination of the shorter '* trailer," reduced to 

 negligible proportions in Gi^ordia virescens and Pylaiella fulvescens 

 (less than | body-length) ; and in such case a residual tractor is 

 curiously complementary to that of the animal sperm with propeller 

 only. The chloroplast-content is reduced to a vestigial eye-spot 

 {Fucus, Dictyota, Laminaria); and the eye-spot may be pale in 



* Sauvageau (1896), Journ. de Bot. p. 185, for Pylaiella fulvescens, Giffordia, 

 p. 119. 



t Bornet (1891), Bull. Soc. Bot. p. 357, for Acinetospora, 



X Retzius compares the mitochondrial mechanism (Nebenkern-system) with 

 that of the sperms of Nemertines and simpler Mollusca of the sea : Biolog. 

 Untersuch. 1906). 



