60 SIPHONEiE. 



Ectosperma clavata Vauch. Hist, des Conf. d'Eau douce, p. 

 34. pi. iii. fig. 10. ; V. Ungeri, M, G. Tliuret, in Annales 

 des Sciences Naturelles ; Berk. Glean. Alg. t. 10.; 

 Harvey, in Manual, p. 149, 



So far from agreeing with M. G. Thuret as to the pro- 

 priety of referring all other species of VauchericB to this one, 

 and constituting a single species of the whole under the 

 name of Vaucheria Ungeri, I am of opinion that V. clavata 

 itself ought not to be regarded as a distinct species, but 

 merely as a condition of almost any one of the numerous well- 

 defined species Avhich have been described. I am led to en- 

 tertain this opinion from having repeatedly observed that 

 the club-shaped extremities are present, terminating many 

 of the filaments of almost all the species which are now 

 recorded, and the distinctness of which cannot for a single 

 moment be doubted. True it is that very many specimens 

 covered with capsules do not present the club-form dilatations 

 of the filaments, and also that these latter are generally pi*esent 

 when the former are altogether wanting. But these facts 

 admit of a rational and interesting explanation, entirely con- 

 sistent with the view here expressed. The specimens of 

 VauchericB furnished with capsules, and those having them 

 not, but possessing the claviform filaments, are usually met 

 with under very different circumstances, the one for the 

 most part in still water, and the other in flowing, such as 

 streams and cascades, that is, the one set of specimens are 

 found in circumstances favourable for the developement of 

 capsules and anthera3, and for permitting the mutual in- 

 fluence, which these organs are supposed to exert on each 

 other, to take place ; and the other kind, or second set, are 

 encountered in localities most unfavourable for these purposes 

 and ends, and in which in many cases it would be impossible 

 for capsules to develope themselves, the filaments being con- 

 stantly washed and pressed upon by the force and weight of 

 the incumbent and flowing waters. This leads to a necessity 

 on the part of Nature, who is so fertile in resources in times 

 of diflftculty and danger, to adopt some other mode of repro- 



