621 SUMMARY OF CTJRKENT RESEARCHES RELATING TO 



diameter, nearly ppberical and inclosed in a firm double membrane. Tboy 

 arc also surrounded by a peculiar stalked envelope of colourless gelatin, 

 wbicb forces itself tbrougb tbe gelatinous envelope of tlie tliallus, and 

 finally becomes detacbed. Tboy arc produced on different individuals 

 from tbe zoospores. 



Witb regard to tbo systematic position of Ht/dnirus, Lagcrheim 

 tbinks tbat it sbould possibly be placed as a diverging branch at the 

 base of tbe Pbajopbycefe. 



Development of Pediastrum.* — Horr E. Askenasy has been able to 

 follow out tbo bistory of development of tbis alga, cbicfly in tbe case of 

 P. Boryanum, and has found it correspond closely to tbat of IJiidrodlrfyon. 

 He fotnid tbis species accompanied by large quantities of a Polyedrium, 

 wbicb be calls P. iwlymorplium, witb a ratber tbiu cell-wall, and spiny. 

 Tbis is a stage in tbe development of Pediastrum Boryanum. Tbo 

 contents of tbe Polycdrium-coll gradually arrange themselves into a disc, 

 its membrane then bursts by a transverse slit, and tbe entire contents, 

 still surrounded by tbe innermost layer of tbe membrane, escape through 

 the slit and assume a globular or ellipsoidal form, tbe macrogonidia 

 being now in active "swarming" movement. Finally they arrange 

 themselves in a plane, invest themselves in a thick membrane, and 

 become a Pediastrum-disc. These coenobia may again produce new 

 coonobia of the same kind, and in either case tbe process is a very rapid 

 one. The usual number of cells in a ccenobium is sixteen, thirty-two, or 

 sixty-four. 



The author believes that a large number of forms hitherto described 

 as distinct species of Pediastrum are in reality but stages in the develop- 

 ment of other species. 



A nucleus can be readily detected in the cells of Pediastrum, as also, 

 in yoimg discs, distinct chromatophores. 



Herr Askenasy has been able to follow the escape of the macrogonidia 

 from the cells of the coenobium ; they are provided with two very short 

 cilia, which are very difiScult to detect. The microgonidia are fusiform 

 in shape, and are provided with two long cilia ; they are gametes, and 

 conjugate witb one another, but not with those which originate from the 

 same cell. The zygotes soon come to rest, surround themselves with a 

 firm membrane, and increase gradually in size from 4 /x to 21 or 24 [x. 

 After a long period of rest they no doubt develope swarm-spores, in the 

 same manner as Hydrodictyon, from which polyhedria are developed. 



The author regards Hydrodictyon and Pediastrum as forming together 

 a single family very nearly related to the Volvociuese. 



Algse parasitic on the Sloth.f — Mdme. Weber van Bosse describes 

 algfe, comprising three new species and two new genera, found as a 

 parasitic growth on tbe hairs of two genera of Tardigrada, Bradypiis and 

 Cltoloejyus. On the side exposed to the light the hairs of these sloths arc 

 completely covered, when living in their natural very moist atmosphere, 

 to the extent of possibly 150,000 to 200,000 individuals on a single 

 hair. 



One of the species is green, and appears to constitute a new genus of 

 Chroolepidese. It has two kinds of reproductive organ, large ovoid 



* Ber. Deutsch. Bot. Gesell., vi. (1888) pp. 127-38 (1 p].). 



t Natuurk. Verhand. Hollaud. Maatsch. Wctcnsch. (2 pis.), 1887. Bee Cot. 

 Cciitralbl.. xsxiv. (1888) p. 161. 



