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 1t may be remembered that the 
oogonia of Pelvetia 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 Cutleriacew. The antheridia are 
known only in Tilopteris and Scaphospora, and occur 
usually as 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 Hetocarpus. It must be remembered that 
the LEctocarpacce supply the closest parallel to the 
Tilopteridacee 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 Bornet bodies to 
which one can have no hesitation in applying the 
term antheridia. These occur in £. secundus and 
in &, Lebelit, and M. Bornct,! in recurring to this sub- 
ject, refers to the grave difficulty it presents to the 
systematist. The antherozoids completely resemble 
those of Fucus, Cutleria and Tilopteris, and we must 
inevitably regard them as possessing the same poten- 
tiality. The absence of a chromatophore and of 
1 Bull, dela Soc. Bot. de France, Tom. 38, 1891, 
