The Structure of Dictyosphceria. \ 7 



The best description known to me of D. favulosa is that furnished 

 by Harvey * : 



'Fronds at first globose, like tubers, heaped together, hollow and empty or 

 filled with sea water, attached to the rock and to each other by a few short, rooting 

 processes; at length irregularly torn, and then forming expanded cartilaginous or 

 skinlike, coarsely reticulated membranes. The membrane is wholly composed of 

 a single layer of large globose, or by mutual compression hexagonal cells, which 

 closely adhere by their sides, leaving the convex ends of the cells free, and these 

 form the surface of the membrane, which when dry resembles a piece of fish skin, 

 or a miniature honeycomb. When the cells have been separated, each is seen to 

 be marked at the line of junction by a double row of circular discs. In full-grown 

 cells the primordial utricle is easily separable from the outer cell-wall, and contains 

 a green granular endochrome, from which by cell division four new cells are 

 formed, and thus the frond extends by repeated quadrisection of its component 



cells I have seen hairlike processes issue from it internally, analogous 



perhaps to the fibrous processes of the membrane of Caulerpa.' 1 



Prof. J. G. Agardh f discusses the structure of Dictyosph&ria at 

 considerable length, with the general result that he does not carry us 

 much farther than Harvey. I should have said that KiitzingJ figures 

 D. favulosa, and attributes to the rows of circular discs (noted above) 

 the character of Keimzellen. There was, no doubt, considerable tempta- 

 tion to take this view, having regard to the affinity of Dictyospharia 

 with Valonia. Agardh deals at some length with these discs, pronouncing 

 against the Kiitzingian view, and, while leaving the matter doubtful, sug- 

 gesting, ' Forsan credere liceret eadem potissimum analoga esse organis, 

 quae in membrana aliarum Siphonearum (Espera, Penicillus] conspiciantur, 

 in quibus deposita calcarea magis normaliter coacervantur.' He also dis- 

 cusses the minute processes projecting into the interior of the cells, while 

 also leaving their nature in doubt. With regard to Harvey's idea, he says : 

 ' Vix cum fibris introrsum prominulis Caulerparum eosdem comparare 

 auderem.' 



D. favulosa occurs in all tropical seas. I have examined material from 

 Ceylon (Harvey and Ferguson), Mauritius (Pike), Red Sea (Hohenacker), 

 Philippines (Challenger Exp.), Barbadoes (Sir R. Rawson and Miss Watts), 

 St. Thomas (Challenger Exp.), Guadeloupe (Maze), and Grenada, collected 

 by myself. The specimens of MM. Maze and Schramm from Guadeloupe 

 called D. valonioides Zan. are D. favulosa. The material principally used 

 is a series of young specimens collected by Ferguson in Ceylon, and my 



* Nereis Bar. Am., iii., p. 50, tab. xliv. B. 



t Till. Alg. Sys/., viii. (Siphoneae), p. 113, tab. 2, figs. 1-3. 



\ Tab. P/iyc., Bd. vii., p. 10, tab. xxv. 



C 



