ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 103 



soon dissolves in water. They are small, biciliated, and provided 

 with an eye-spot. They conjugate, but in a manner different from 

 other algae, uniting by the end which does not bear the cilia. The 

 zygospore becomes invested, in the course of a few days, with a cell- 

 wall ; the further development of the resting-spore was not observed. 

 Those zoospores which do not conjugate, develope asexually in the 

 ordinary way. After a time the terminal cell of the filament breaks 

 up into from four to eight cells, which become detached, and present 

 a protococcoid appearance. They develope, on germinating, into the 

 original tufts, each cell putting out from two to four germinating 

 filaments. He proposes to place this genus in his new class of 

 Chroolepidaceae (see p. 106). 



Ctenocladus. — The only species, C. circinnatus, forms green incrus- 

 tations in brackish marshes, composed of densely crowded tufts. The 

 prostrate, curved, and segmented filaments put out a number of 

 short segmented branches, which are all beautifully curved. These 

 branches again branch, but the branches are borne on one side only. 

 The cells contain homogeneous chlorophyll, a starch-grain, and a 

 true nucleus ; the wall is divided into three layers, the outermost of 

 which presents the reactions of cuticle. Asexual reproduction takes 

 place by means of macrozoospores and microzoospores. , The macro- 

 sporangia are very elongated cells in the branches, or sometimes cells 

 which put out a long lateral protuberance. The zoospores, from 

 four to thirty-two in number, are forced out through a narrow opening 

 in the wall of the mother-cell. They have the ordinary form of 

 biciliated zoospores, and germinate into the new tufts after swarming 

 for about twelve hours. After the discharge of the macrospores the 

 thallus assumes a hibernating condition. The cells become rounded 

 off, many of them divide, and the common cell-wall is gradually ab- 

 sorbed, so that the tuft becomes changed into an irregular aggregation 

 of cells imbedded in mucilage, a protococcoid colony resembling a 

 Palmella or Gloeocystis. These palmelloid cells produce the micro- 

 zoospores, from four to sixteen in a cell. They resemble the macro- 

 zoospores, except in size ; their behaviour on germination was not 

 observed. Sometimes the hibernating cells which do not give birth 

 to microzoospores enter on a new condition ; they develope into 

 filaments closely resembling a TJloihrix, which form a kind of hypo- 

 thallus. In these, shorter dark green cells are formed which develope 

 into the typical tufts of Ctenocladus. But while these tufts mostly 

 pass over in autumn into the hibernating condition already described, 

 some cells, which Borzi calls " zoogonangia," enlarge greatly, assume 

 a pear-like form, and hibernate in this condition. From these are 

 produced in the spring biciliated zoospores, which conjugate ; but 

 conjugation takes place only between zoosj)ores from different zoogo- 

 nangia. The author considers the genus as probably a highly 

 specialized form of the Chroolepidacese. 



Physocytium. — The only species, P. confervicola, was found growing 

 on CEdogonium and Cladophora. It forms small colonies attached to 

 the substratum by a delicate filament. Each colony is composed of 

 from 1 to 32 ciliated cells inclosed in a vesicle of very fluid mucilage, 



