REJUVENESCENCE IN NATURE. 185 



formed in like manner by repeated division of the cell- 

 contents, break through the mother-cell of Cystococcus* 

 Characium^ and Ectocarpus,\ Very numerous swarm- 

 ing-cells, not formed by successive division of the green 

 contents, but by simultaneous division of the mucila- 

 genous layer alone, issue through irregular lateral 

 bursting of the parent tube in Ascidium (p. 128), Hy- 

 drodictyon,^ Chcetomorpha area,\ Bryopsis ;^[ through 

 tearing open of the apex of the tube in the genus 

 Derbesia** separated by Solier from Bryopsis, as also in 

 Saprolegniaferax, K. (Achlya prolifera^} Nees.) ; by a 

 hole formed regularly at the upper margin of the cell in 

 Cladophora ;JJ by a most elegant, lid-like dehiscence in 

 certain species of the genus Chytridium^ parasitical on 



* Nageli, ' Einzell. Algen,' p. 84, t. iii, E. 



f Ibid., p. 86, t. iii, D. 



J Crouan, ('Ann. des Sc. nat.,' 1839, p. 248, t. v). According to 

 Thuret, ('Ann. des Sc. nat.,' 1845, p. 274), the gonidia of this genus have 

 two cilia. 



In particular from these cells in which no new net is formed, (see 

 above, page 137. 



|| According to J. Agardh. ('Aim. des Sc. nat.,' 1836, p. 194, t. xii, 



' J[ Ibid., 1. c., p. 200, t. xii, f. 9. 



** 'Ann. des Sc. nat.,' 1847, t. vii. The genus Derbesia includes -ffryo/wts 

 lenuissima and Lamourmtxii of authors, the fertile branchlets are shorter and 

 more inflated than in Bryopsis, they let the mass of the germ-cells escape at 

 once by bursting at the apex, while in Bryopsis, according to Agardh, the 

 germ-cells escape singly by a small, lateral, nipple-like and outwardly pro- 

 jecting orifice. The germ-cell of Derbesia possesses a wreath of cilia, like 

 those of (Edogonium. 



ft Vide linger, 'Eiuiges zur Lebensgeschichte der Achyla prolifera,' 

 ('Linnaea,' 1843, p. 129, t. iv.) I have repeatedly observed the mode of 

 origin of the gomdia from the mucilaginous layer of the fructifying end- 

 cell ; I could only detect a single, short cilium, while Thuret describes two. 



JJ According to observations on Cladophora glomerata, (June 1847), and 

 fracta, (August 1847). Meyen observed the birth of the active spores in the 

 former species, (' Nov. Acta.,' t. xiv, ii, p. 445, t. xxvii, f. 5, 6.) In regard 

 to the number of cilia my observations agree with Thuret's ; I found two in 

 C. glomerata. 



' The Chytridia form a new genus of unicellular, parasitical Algae, or, if it 

 be preferred, of aquatic Fungi, related to Saprolegnia about as much as 

 Ascidium is to Bryopsis. The entire plant is composed of a single, balloon- 

 shaped cell, which penetrates into the Algae upon which it grows by a more 

 or less developed root-like base. The inflated portion of the cell is filled 

 with colourless mucilage, from which are formed, not through successive 



