UEJUVENESCENCE IN NATURE. 289 



conceivable that Hassall's strange Mesocarpus notabilis* 

 belongs here; this would require the assumption, that 

 the uniting canal, becoming filled with the contents of 

 the two conjugated-cells, pushed aside completely the 

 septum between them. 



/3. The spore in one half of the double-cell (in the 

 cavity of one of the mother-cells). This is the case in 

 Hassall's second division of the 8pirogyr(je,\ which 

 Kiitzing has distinguished as a pecuhar genus, under 

 the name of Ithynchonema.\ 



d. Lateral, parallel union of isolated cells. — Here 

 belongs the conjugation of Closterium Lunula (see p. 140), 

 in which, according to Morren's express statement, § 

 three different membranes take part in the formation of 

 the canal of union, an inner and an outer cell-membrane, 

 and a membrane (the primordial utricle) immediatiely 

 enclosing the green mass. The globular reproductive- 

 cell formed in the connecting canal, is an active gonidium, 

 which begins to revolve even while within the canal, and 

 soon breaks through the gelatinously swollen membrane 

 of the latter. Very often two approximated individuals 

 divide again and conjugate before they have become 

 completely separated : whence result conjugated double- 

 pau'S.II According to Ralfs' description of the conju- 

 gation of Penium Jenneri, it resembles that of CI. Lunula, 

 a large globular spore being formed in the interior of a 

 connecting canal, narrow at the points of issue, like 

 that of Mesocarpus.*i 



* Hassall, 1. c, t. 46. 



f Hassall, 1. c, p. 152, t. 33 and 34; Nageli, 'Algensysteme,' p. 151, 

 t. iii, f. 22—25. 



J ' Spec. Alg.,' p. 443. The genus Bhi/nchonemn, although based on a 

 very remarkable character, is scarcely natural, smce both kinds of conjuga- 

 tion sometimes occur in one and the same species. I have observed this 

 especially in Spirogyra Weberi, in which, however, the chain-union is more 

 common than the yoke-union. 



§ ' Mem. sur les Closteries,' ' Ann. des Sc. nat.,' 2 ser., v, 325, t. 9 

 (1836.) (See also Smith, on Closterium, 'Annals of Nat. History,' sec. ser. 

 vol. V, p. 8, t. i.— A. H.) 



11 Morren, 1. c, t. 9, f. 22, 23, (Smith, 1. c.) 



f Ralfs, 1. c, p. 153, t. 33, f. 2. 



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