REJUVENESCENCE IN NATURE. 179 



which, as in Glceocapsa, appear to be separated by inter- 

 mediate layers of softer jelly, whence arises a distinctly 

 concentric structure of the envelope. But the enveloping 

 layers of Urococcus do not retain their original form and 

 integrity ; not increasing themselves in size, they are 

 pushed off on the upper side by constantly succeeding 

 inner coats, being at first merely attenuated at one side, 

 but subsequently, as it seemed to me, actually broken 

 through. Since this emergence from the old coats is 

 always repeated on the same side, ti membranous-gela- 

 tinous peduncle is produced, formed of cups fitted one into 

 another, so as to give an annularly streaked, apparently 

 shortly articulated aspect. The red cell, which occupies 

 the summit of this peduncle, sometimes divides, and 

 this of course produces a subsequent dichotomy of the 

 peduncle. If the periods of the formation of the separate 

 enveloping layers were known, the age of the little plant, 

 whose history is preserved in the gelatinous peduncle, 

 might be determined by the number of rings. As a last 

 example to be included here, I may mention the forma- 

 tion of the so-called veil of Zonaria Pavonia* The fan- 

 shaped thallus of this Alga possesses two unlike surfaces, 

 one of which, the outer or back surface, in reference to 

 the early unrolhng of the thallus, is clothed with a layer 

 of smallish cortical-cells, these becoming coated with a 

 thickish membranous layer, comparable to the cuticle of 

 higher plants, by more active development of membrane 

 on the side next the surface. From these cortical-cells are 

 developed the fructification-cells and paraphyses, in 

 alternating zone-like collections {sori). The former 

 originate from a division of the cortical-cells, parallel to 

 the surface of the thallus, into two unlike daughter-cells, 

 the lower of which retains the character of a cortical-cell, 

 while the upper emerging from the surface of the thallus, 

 becomes the mother-cell of the spore ;t the latter (the 



* Vide Kiitzing, 'Pliyc. Gen.,' t.xxii, 1, and Nageli, 'Algensyst.,' p. 180, 

 t. V, f. 2, 3, 7. 



t Kiitzing and Nageli regard this as the seed-cell itself, (" Spermatium," 



