Grubb. — The Attachments of Porphyra umbilicalis. 135 
the threads now become awl-shaped with the nuclei aggregated at the apex, 
which is protected by a swollen wall, suggesting that a boring action is 
necessary if the dense tissue of the disc is to be penetrated. 
The disc filaments may be simple or branched, branching as a rule 
taking place at a swelling and characteristically forming distinct two-armed 
structures with barbed inner edges having the appearance of clasping organs 
(Text-fig. 3, D). More rarely a new structure in the shape of a miniature 
hapteron has been dissected out, and in two cases this consisted of five long 
arms terminating a filament and themselves branching again at the tips 
Text-fig. 3. Outline drawings showing the modifications undergone by the filaments of the 
disc. A and B. Sucker and runner formed as attachment to the rock. C. A swollen multinucleate 
tip. D. A branching tip. E. Hapteron structure with five long arms. F. A group of cells cut off 
at the tip of a filament. Camera lucida drawings, x 750. 
(Text-fig. 3, E). In other cases the hapteron was in a rudimentary state, 
a filament ending in short blunt arms which were arranged in more than 
one plane with regard to the substratum. On finally reaching the sub¬ 
stratum other modifications may take place; the filament may creep along 
at right angles to its former course, here and there putting out suckers 
which establish a connexion with the rock (Text-fig. 3, A and B). More 
often the tip or some other portion swells up to give a multinucleate organ 
(Text-fig. 3, C), which often attains a great size, and may divide up to give 
cells which are clamped to the ground by their gelatinous walls (Text-fig 
3, f). The variety of forms assumed by these modified filaments is endless 
