246 SCIENCE PROGRESS. 



and to ascertain whether, after all, the gulfs that have been 

 fixed between certain orders are so wide as we are prone to 

 believe. But for the absence of conceptacles, to which 

 perhaps less weight may be attached from considerations I 

 have submitted, the male and female sori of Cittleriacece 

 have a strong resemblance to those of Fucacece. There is 

 the further deeply interesting fact of the occurrence of non- 

 sexual sporangia in this order, a mode of reproduction 

 absent from the Fucacecs. The unfertilised oosphere is 

 ciliated unlike that of the Fucacece, but it is not impregnated 

 until it has come to rest, and it is considerably larger than 

 the antherozoids. It is customary to mark off these groups 

 (and sometimes the Tilopteridacetz with them) from the 

 Pliceosporece, i.e., the remainder of the olive-brown sea- 

 weeds (except Dictyotacece), and for purposes of classification 

 this is of course necessary, but among the Phceosporecz 

 interesting types emerge which suggest at least continuity. 

 The genus Myriotrichia (9), for which it is difficult to find 

 a proper home, has unilocular sporangia of the ordinary 

 kind, but its plurilocular sporangia, which give rise to the 

 conjugating gametes, are exceptional. There are differences 

 of size among them, and this difference is but the outward 

 expression of the nature of their contents. As a rule 

 the small sporangia (or gametangia) give rise to four 

 large gametes, and the others to eight, but the number 

 varies from six to twelve. The interesting point is that 

 conjugation takes place only between a large gamete and a 

 small one, and apparently either while motile or at the 

 moment of coming to rest. The large one appears to 

 absorb the small one, and soon nothing but the two pig- 

 ment spots remain to mark their former separate existence. 

 We have here a preservation of the difference of size. 

 Looked at simply from the point of view of conjugation 

 Cutleria is a link between the types of Fucus and of 

 Myriotrichia. The better-known case of Ectocarpas sili- 

 culosus offers another exception to the rule of equal con- 

 jugation of gametes. Here the female gamete first comes 

 to rest, and is then surrounded by numerous male gametes, 

 one of which succeeds in conjugating with the female 



