INTRODUCTION. 27 



disposed in starlikc forms, and sometimes in spires, a number 

 of vesicular bodies, the immature zoospores, and in these it is 

 that the colouring matter of the plant chiefly resides. It is 

 from this viscid fluid, the quantity of which is so consider- 

 able, that the Conferva derives its nourishment and means of 

 increase, and not, at least so I consider, from the intercellular 

 substance of Mohl, to whose theory an objection occurs to my 

 mind, in the fact that it is not rational to suppose tliat the 

 nutritious fluid should be placed external to the cavities of 

 the cells, the contents of which it is destined to nourish. 

 Such is the view usually entertained, I believe, of the 

 general structure of the filamentous Algce. The opinion 

 at present held by Mr. Jenner as to their organization differs 

 considerably from that just stated, that gentleman declaring 

 that he has, in the Zygnemata^ detected a third membrane of a 

 delicate and homogeneous appearance, and that it is by this that 

 the dissepiments are formed, and not by the second, which 

 terminates just at the situation of the joints, between which 

 it does not send down any partition walls. Thus the outer 

 membrane he describes as continuous, the second as a series 

 of short tubes, open at their extremities, placed end to end, 

 and the third as the true cells. Of the accuracy of this 

 ingenious view of the structure of the filaments of the 

 Zygnemata, &c. I have not as yet been able to satisfy myself. 

 The investing membrane of the cells, one would suppose, 

 would be essential to the existence of a Conferva ; yet M. 

 Areschoug, in an excellent article on Hydrodictyon pentagonum, 

 states that that curious production does not possess it. In 

 the UlvacecB the cells are not usually placed in linear series, 

 but are scattered through a gelatinous substance, which is 

 usually furnished with an investing membrane. 



As the different cells of a Conferva do not communicate 

 directly with each other, each cell may therefore be regarded 

 as possessing a separate and independent existence, inasmuch 

 as it contains all the parts requisite for the formation of an 

 entire Conferva. A Conferva then may be regarded, like the 

 associated Zoophyte, as a compound or aggregated being ; and 

 it is to this aggregation of similar parts that the Confervce owe 



