248 SCIENCE PROGRESS. 



The absence of active mobility, however, is most in- 

 teresting when we come to consider the case of Dictyotacecz. 

 Some authors have sought in them a link with the Fioridecs, 

 and most now go so far as to assign them a place apart 

 pointing towards Floridece. This view is based on the 

 unciliated character of all the reproductive bodies, the 

 resemblance of the motionless antherozoids to the spermatia 

 or pollinoids of Floridece, and the division into four of the 

 spores constituting a likeness to the tetraspores of the same 

 group. The contention really rests on no more than this 

 slender support, and the absence of any observation of 

 fertilisation leaves the field open for speculation. We 

 have seen in Ectocarpus pusillus a lack of mobility in the 

 contents of the plurilocular sporangia which is a fair parallel 

 to the motionless antherozoids, if I may so term them, of 

 Dictyotacecz. Then as for the so-called tetraspores, they 

 are extruded without a membrane, though they soon secrete 

 one. But their condition on emission is, to say the least, 

 just as consistent with loss of cilia as with loss of mem- 

 brane ; it is a physiological condition of which too much 

 can readily be made. As for the number — four — which 

 has suggested the comparison with the tetraspores of the 

 Floridece, even that is inconstant. The prevailing number 

 is certainly four, but frequently only two, or rarely, one. 

 No trichogyne or corresponding body has been observed, 

 and the sorus of presumptive female reproductive bodies 

 answers very much better for degenerate Phceophycece than 

 for Fioridecs. The presumptive oogonia are motionless, 

 so are the corresponding bodies in Tilopteridacece, so are 

 the oospheres of Fucacece. The character of the vegetative 

 organs is overwhelmingly in favour of PhceopJiycece. The 

 Diciyotacece in fact are most interesting when compared 

 with CutkriacecB, in which all three kinds of reproductive 

 bodies are ciliated. The growth of the thallus is certainly 

 different, since in Cutleria it is trichothallic. But it may 

 be recalled that the growth of the Aglaozonia or non-sexual 

 forms of Cutleria is not trichothallic but by marginal initials. 

 It would, moreover, be unwise to insist too much on this 

 when we remember the tuft of hairs at the apical dimple in 



