EXPLANATION OF PLATES XV 



PLATE VI. (Facing p. 550) 



SEXUAL GENERATION OF VOLVOX GLOBATOR. (After Cohn) 



Fig. 1. Sphere of Volvox globator at the epoch of sexual generation : a, 

 sperm-cell containing cluster of antherozoids ; a 2 , sperm-cell showing side- 

 view of discoidal cluster of antherozoids ; a 3 , sperm cell whose cluster has 

 broken up into its component antherozoids ; a 4 , sperm-cell partly emptied by 

 the escape of its antherozoids; 66, flask-shaped germ-cells showing great 

 increase in size without subdivision ; 6 2 , 6' 2 , germ-cells with large vacuoles in 

 their interior ; 6 3 , germ-cell whose sh^,pe has changed to the globular. 



Fig. 2. Sexual cell, a, distinguishable from sterile cells, 6, by its larger 

 size. 



Fig. 3. Germ-cell, with antheroids swarming over its endochrome. 



Fig. 4. Fertilised germ-cell, or oosphere, with dense envelope. 



Fig. 5. Sperm-cell, with its contained cluster of antherozoids, more 

 enlarged. 



Figs. 6, 7. Liberated antherozoids, with their flagella. 



PLATE VII. (Facing p. 553) 



OSCILLARIACE^E AND SCYTONEMACE^ 



Fig. 1. Lyngbya fcstuarii, Lieb. x 160. 



Fig. 2. Spirulina Jenneri, Ktz. x 400. 



Fig. 3. Tolypoilirix cirrhosa, Carm. x 400. 



Fig. 4. Oscillaria insignis, Thw. x 400. 



Fig. 5. O. Frolichii, Ktz. x 400. 



Fig. 6. O. tenerrima, Ktz. x 400. 

 These figures are after Cooke. 



PLATE VIII. (Facing p. 554) 



DESMIDIACEJE, RIVULARIACEJS, AND SCYTONEMACE^ 



Fig. 1. Zygosperm of Micrasterias denticulata, Breb. (After Ealfs.) 



Fig. 2. Cosmarium Brebissonii, Men. (After Cooke.) 



Fig. 3. Euastrum pectinatum, Breb. (After Kalfs.) 



Fig. 4. Zygosperm of Staurastrum hirsutum, Breb. (After Ealfs.) 



Fig. 5. S. gracile, Ealfs. (After Cooke.) 



Fig. 6. Xanthidium aculeatum, Ehrb. (After Ealfs.) 



Fig. 7. Rivularia dura, Ktz. (After Cooke.) 



Fig. 8. B. diira, Ktz. x 400. (After Cooke.) 



Fig. 9. Seytonema natans, Breb. x 400. (After Cooke.) 



Fig. 10. Stanrastrum hirsutum, Breb. (After Cooke.) 



PLATE IX. (Facing p. 580) 



DESMIDIACE^ 



Fig. 1. Micrasterias crux-melitensis, Ehrb. (After Cooke.) 



Fig. 2. Closterium setaceum, Ehrb. (After Cooke.) 



Fig. 3. Desmidium Swartzii, Ag. (After Cooke.) 



Fig. 4. Penium digitus, Ehrb. (After Cooke.) 



Fig. 5. P. digitus, Ehrb. (transverse view). 



Fig. 6. Spirotcenia condensata, Breb. (After Cooke.) 



Fig. 7. Docidium baculum, Breb. (After Cooke.) 



Fig. 8. Gonatozygon Brebissonii, De Bary, conjugating. (After Cooke.) 



PLATE X. (Facing p. 593) 



PLEUROSIGMA ANGULATUM 



This is a direct photo-micrograph, taken by Dr. E. Zeiss, as magnified 4900 

 diameters. We direct attention specially to it as giving evidence of the pre- 

 sence (however originated) of the intercostal markings, which may be seen 

 with considerable clearness on the right-hand side of the midrib and in the 

 middle of the valve. 



