186 NOTES AND MEMORANDA. 



gain in any of their details, and seem consequently not to move in 

 space. In Microscopes of liigh magnifying power, the tenuity of the 

 pencils of rays which start from every point of the imago also contributes 

 to make its position in space uncertain to the eye, since the accommoda- 

 tion is no longer necessary in order to see it tolerably clearly. How- 

 ever, it none the less exists in a definite place in space, where we must 

 go to measure it in order to know the true amplification ; and here 

 again the megameter can be employed with advantage. 



Discosporangium, a new genus of Phaeosporese.— The fact that 

 the majority of Phfeosporea3 are only to be met with during a portion 

 of the year, led M. Falkenberg (at the Naples Zoological Station) * 

 to the conjecture tliat they may at certain periods withdraw themselves 

 to great sea-depths. Although this conjecture was not confirmed, it 

 led to the discovery of a new genus at a depth of 15 metres, off Cape 

 Misenum. This sea-weed, to which Falkenberg gives the name 

 Discosporangium svhtile, consists of filaments of cells growing by an 

 ai)ical cell. They have lateral branches, springing from the middle 

 of the cells of the filament. The origin of the sporangia (zoo- 

 sporangia) is the same. They are placed solitary at the centre of the 

 cells, and form a unilamellar square plate, the compartments of which 

 open, when ripe, on the upper side of the sporangium. The furtlier 

 development of the zoospores was not observed. The author suggests 

 that the zoospores produced in unilocular and plurilocular sporangia 

 of the PhfeosporesB perform different functions. Although the sys- 

 tematic position of Discosporangium is still doubtful, Falkenberg 

 considers its nearest ally to be Choristocarpus, a genus separated 

 from the Ectocarpese by the mode of development of the thallus. In 

 the course of his researches the author had the opportunity of con- 

 firming the observations of Sirodot on the genetic connection of 

 Chantransia and Batracliospermum. He also gives a list of a con- 

 siderable number of species of marine Floridete which bear on the 

 same individual both tetraspores and capsular fruits, as, for instance, 

 species of Callitliamniun and Polysiplionia. 



Reproduction of Ulvacese. — The reproduction of three species, 

 Monostroma hullosum, Tetraspora lubrica, and Ulva rigida has been 

 studied by J. lieinke.l In the first-named species he observed the 

 formation and conjugation of the zoospores, the development of the 

 resulting zygospore into a resting sj)ore, and the subsequent con- 

 version of the latter, by division of its contents, into a young 

 31onostroma thallus. The non-sexual reproduction of the plant was 

 also observed. 



The observations on Ulva rigida showed that in this species also 

 new individuals are produced from resting spores without the inter- 

 mediate formation of zoospores. 



In Tetraspora luhrica the macrozoospores, after a short free ex- 

 istence, settle down and divide into four-, the daughter-cells being 

 either all in one plane, or arranged tetrahedrally. Multiplication 



* ' Mittheihmgcn der Zoologischen Station zu Neapcl,' vol. i. (1878) p. 51. 

 t ' Jalirb. f. wis3. Bot.,' vol. xi. (1878) p. 531. 



