408 Delf . — The Attaching Discs of the Ulvaceae. 
a typically coenocytic group such as the Siphonales. The method of 
formation of the disc, indeed, resembles far more closely that found in the 
simplest red seaweeds, such as Bangia and Porphyra , but whether this is 
a case of true affinity, or of parallel development in widely different groups, 
must be decided only on the result of further research. 
The apparently parasitic penetration of the disc filaments into the 
tissue of some other Algae, and the way in which they appear to entirely 
take possession of the cells of the host, are, as far as I know, unparalleled at 
present amongst the Chlorophyceae. 
PLATE XLV. 
Illustrating Miss Delf’s paper on the attaching discs of Ulva. 
All the figures were drawn with a No. 3 eyepiece (Swift) and D. D. objective (Zeiss), excepting 
Figs. 7 and 8, which were drawn with a No. 4 compensating ocular (Zeiss) and apochromatic 
objective (Swift). 
Fig. 1. Part of a single filament teased from just above the disc, x 510. 
Fig. 2. The tip of a disc filament with two nuclei. x 510. 
Figs. 3 and 4. Disc filaments from a teased preparation, showing irregular branching, x 510. 
Figs. 5 and 6. Cell-divisions in filaments which had reached the periphery of a disc, x 510. 
Fig. 7. Part of the periphery of a disc, showing large and small filaments, x 510. 
Fig. 8. Part of the stipe in longitudinal section, showing filaments extending within the surface 
of the thallus and (a) forming a small-celled tissue externally, x 510. 
Figs. 9 and 10. Small part of the periphery of the cross section of a seaweed resembling 
Polysiphonia , infested with filaments from an attached disc of Ulva. apochromatic.) 
