of the Freshwater Algae. 25 



other spores. The great similarity in the structure of the inci- 

 pient spores in the genus Anthoceros with that of the radiated 

 organs in Zygnema, would lead to the supposition that they were 

 identical in their nature ; so far however from this being the case, 

 I consider that all analogy between them terminates with the out- 

 ward resemblance. The difficulties in the way of regarding the 

 structure in Zygnema as an incipient germ or spore appear to me 

 to be insuperable; for the question would immediately arise, where- 

 fore is it, that since the contents of two cells generally go to form a 

 single spore in the genus Zygnema, and since this radiated organ 

 is present in every cell, that the one is suppressed, while the other 

 is destined to give birth to the future Zygnema ? Supposing how- 

 ever a satisfactory solution of this difficulty to have been made, 

 still another arises. It is far from being an incontrovertibly esta- 

 blished fact, that the elliptical body formed in Zygnema by the 

 concentration of the matter of two cells, and usually denominated 

 a spore, does really contain but a single germ. It is far more 

 consistent with known facts to suppose that they are sporangia 

 filled with fertilized sporules ; for this is certain, that numerous 

 zoospores are formed within each cell, and which may even be 

 seen through the membrane of the sporangia themselves by the aid 

 of a good glass, these zoospores being also identical with the bril- 

 liant granules of the Algse. 



The highly interesting observations of Mohl on the genus An- 

 thoceroSy the accuracy of which is in no respect questioned by me, 

 do not therefore occasion any modification of the views expressed 

 of the functions of the radiated organ in Zygnema. 



On Tubular or Vascular Structure in the Freshwater Alga. — 

 In the genera Vesiculifera, Zygnema, Microspora, and doubtless 

 in many other Algse, the zoospores up to a certain period of the 

 development are connected with each other, and probably with 

 the central cytoblast, by means of a tubular or vascular network, 

 in the angles formed by which the zoospores are situated. This 

 structure is most manifest in Conferva crispata and its allies (see 

 fig. 8), and requires, in order that it may be clearly seen, that the 

 development of the species should be considerably advanced and 

 the zoospores somewhat scattered. It may, generally, however be 

 easily detected in the genera Vesiculifera and Zygnema : in the 

 latter the tubular formation is not arranged in a reticulated man- 

 ner, but occupies the centre of each spiral thread (PI. I. fig. 1, 2,3). 

 It is by the inosculation of the tubular radii given oiF by the cen- 

 tral cytoblast with this vascular structure that a direct commu- 

 nication is established between that organ and the zoospores : now 

 presuming that the cytoblast in the other Algse in which it occurs 

 presents at some period of its existence a similar formation to 

 that which it exhibits in the genus Zygnema, and adopting the 



