Fresh- Water Algce of Canaaa. 46 1 



The endocbrome is arranged in the form of spiral threads, as may 

 be seen in Figs. 4 and 5; tbe number of spires varying from one 

 to eigbt, and the number of threads from one to six. These spiral 

 cords are tubular, and contain at intervals, united together by a 

 delicate cord, brilliant granules, which Mtiller, in his surprise on 

 first discovering a species of the genus, likened to precious stones 

 European naturalists have divided them into two sub-genera, in 

 one of which the filaments unite, as in Fig. 4, and in the other no 

 such conjugation takes place. 



The structure of the joints of some species of the Zygnema has 

 been a subject of special observation by European naturalists. 

 Mohl, quoted by Hassall, says that " In Z. elongatum (Ag.) the 

 dissepiments have a very peculiar structure which I have found 

 in no other species. The terminal surface of each cell is not even, 

 but elongated into a blunt conical process. This process can only 

 be observed in its true state when two joints are separated one 

 from the other ; when on the contrary the threads are unbroken, 

 the process is generally introverted, like the finger of a glove. 

 This is the common condition, and in most threads no joint is 

 found otherwise constructed." It is not quite accurate to say 

 that the eversion is only truly observed when two joints are sepa- 

 rated. Hassall remarks that it has nothing whatever to do with 

 the separation of the cells, but depends upon the unequal internal 

 pressure of the granular contents which occurs chiefly at the period 

 of reproduction. 



Z. curvatum. Hass. 



" Char. — Filaments nearly equal in diameter to those of Z. ne- 

 glectum. Conjugation angular. Cells three or four times as 

 long as broad, coalescing without the intervention of transverse 

 tubes. Spires about four in number, faintly indicated. Spo- 

 rangia ovalP Hass. 



Habit. — In pools at Moffatt's Island, St. Lambert, Montreal. 



This species is remarkable for the direct conjugation of the 

 cells without the intervention of tubes, and is the only species of 

 the genus that does so. By this junction the filaments become 

 geniculate, or bent at angles more or less obtuse, a very good 

 idea of which may be obtained by bending the middle joint of 

 a finger on each hand and bringing the knuckles together. 



