SIPHONACE.E : HYDRODICTYON. 329 



plant forms ' resting- spores ' also, like those of Vaucheria ; and 

 there is every probability that they are generated by a like Sexual 

 process. They may remain unchanged for a long time in water 

 ■when no appropriate nidus exists for them ; but will quickly germi- 

 nate if a dead Insect or other suitable object be thrown in. 



248. One of the most curious forms of this group is the Hydro- 

 diet yon utrieulatum, which is found in fresh-water pools iu the 

 midland and southern counties of England. Its frond consists of 

 a green open network of filaments, acquiring, when full-grown, a 

 length of from four to six inches, and composed of a vast number 

 of cylindrical tubular cells, which attain the length of four lines or 

 more, and adhere to each other by their rounded extremities, the 

 points of junction corresponding to the knots or intersections of 

 the network. Each of these cells may form within itself an 

 enormous multitude (from 7,000 to 20,000) of Gronidia ; which, at 

 a certain stage of their development, are observed in active motion 

 in its interior ; but of which groups are afterwards formed by their 

 mutual adhesion, that are set-free by the dissolution of their en- 

 velopes, each group, or ' Macro -gonidium,' giving origin to a new 

 plant-net. Besides these bodies, however, certain cells produce 

 from 30,000 to 100,000 more minute bodies of longer shape, each 

 furnished with four long cilia and a red spot, which are termed 

 1 Micro-gonidia : ' these escape from the cell in a swarm, move 

 freely in the water for some time, and then come to rest and 

 sink to the bottom, where they remain heaped in green masses. 

 It appears from the more recent observations of Pringsheim 

 (" Quart. Journ. of Microsc. Science," N. S., Vol. ii. 1S62, p. 54), 

 that they become surrounded with a firm cellulose envelope, and 

 may remain in a dormant condition for a considerable length of 

 time, bike the ' statospores ' of Volvox (§ 197) ; and that in this 

 condition they are able to endure being completely dried-up with- 

 out the loss of their vitality, provided that they are secluded from 

 the action of Light, which causes them to wither and die. In this 

 state they bear a strong resemblance to the cells of Protococcus. 

 The first change that manifests itself in them is a simple enlarge- 

 ment ; next the endochrome divides itself successively into distinct 

 masses, usually from two to five in number ; and these, when set 

 free by the giving- way of the enveloping membrane, present the 

 characters of ordinary Zoospores, each of them possessing one or 

 two vibratile filaments at its anterior semi-transparent extremity. 

 Their motile condition, however, does not last long, often giving 

 place to the motionless stage before they have quite freed them- 

 selves from the parent-cell ; they then project long angular pro- 

 cesses, so as to assume the form of irregular polyhedra, at the 

 same time augmenting in size ; and the endochrome contained 

 within each of these breaks-up into a multitude of Gonidia, which 

 are at first quite independent and move actively within the cell- 

 cavity, but soon unite into a network that becomes invested with a 



