68 SEAWEEDS 



regard these bodies as oogonia, the objection arises 

 that they are set free, in two of the genera, enveloped 

 in a wall ; but it may be remembered that the 

 oogonia of Pclvetia have a persistent inner gelatinous 

 wall which does not prevent fertilisation. The view 

 is also tenable and more probable that they are 

 parthenogenetic, a condition said to occur occa- 

 sionally in the Cutler iacccc. The antheridia are 

 known only in Tilopteris and Scaplwspora, and occur 

 usually a,s intercalary bodies on the branches. They 

 arise by radial and transverse divisions, and are 

 elongated, hollow cylinders composed of tiers of 

 small cells, each of which gives rise to a ciliated 

 antherozoid. 



The difficulties of interpretation in the case of 

 these presumptive oogonia and antheridia are much 

 increased by the occurrence of aberrant species in 

 the genus Ectocarpus. It must be remembered that 

 the Ectoearpacecc supply the closest parallel to the 

 Tilqiteridacece in respect of the morphology of the 

 thallus. Besides the unilocular and plurilocular 

 sporangia characteristic of Ectocarpus, there have 

 been recorded by MM. Thuret and Bornct bodies to 

 which one can have no hesitation in applying the 

 term antheridia. These occur in E. sccundus and 

 in E. Lebelii, and M. Bornet, 1 in recurring to this sub- 

 ject, refers to the grave difficulty it presents to the 

 systematist. The antherozoids completely resemble 

 those of Fucus, Cutlcria and Tilopteris, and we must 

 inevitably regard them as possessing the same poten- 

 tiality. The absence of a chromatophore and of 



1 Bull, de la Soc. Bot. de France, Tom. 38, 1891. 



