28 INTRODUCTION. 



their very elegant and beautiful appearance under the micro- 

 scope. Much of the beauty of those most interesting of all 

 Nature's works, the Zoophytes, arises from the same cause. 



Connecting the zoospores with each other, we find in most 

 of the Conferva a vascular structure. (See PL 17.) In the 

 genera Vesiculifera, Zygnema, Microspora*, and doubtless 

 in many other Alga, the zoospores up to a certain period 

 of the developement 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, and requires, in order that it may be 

 clearly seen, that the developement 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 manner, but occupies the 

 centre of each spiral thread. It is by the inosculation of the 

 tubular radii given oif by the central cytoblast with this 

 vascular structure, that a direct communication is established 

 between that organ and the zoospores. f 



In addition to the membranes above described, the zoospores, 

 with the vascular network, the sporangia, and the central cyto- 

 blast, two other organs have been noticed in the Conferva, 

 first by Mr. Bowerbank in a species of Zygnema, which I 

 transmitted to him, and subsequently by myself in a variety 

 of other species. The one is cruciform and adherent to the 

 Id interior wall of the cell. (See PI. 17. fig. 1, 2, 3.) It (Mr. 

 Bowerbank remarks) " is the vegetable structure which 

 secretes the raphides." They are probably not definite organs, 

 but crystals. The other body is small, elongated, somewhat 

 curved, and attached to, or lying upon, the plant. (See PI. 17. 

 fig. 1,2,3.) This (Mr. Bowerbank observes) is certainly " a 

 string of minute cytoblasts ; and similar bodies, but more 



* Cladophora Kiitzing. 



f See " Annals and Magazine of Natural History," vol. xii. p. 20., for a 

 paper entitled, " Observations on some Points in the Anatomy and Phy- 

 siology of the Freshwater Confervas." 



