394 
PROF. J. D. F. GILCHRIST N DIMORPHISM AND 
successive fragmentations or proliferations at the extremity of the tail : (4) a 
further difference is that, though the two\species were found in the same 
locality and under the same conditions, they do not usually occur at the same 
season, P. capensis being found chiefly, often exclusively, in the winter 
months, F. proliferans in the summer months, a fact which may, however, 
indicate a possible relation between the two species. To determine this point 
extensive collections were made at various seasons, but no indication of any 
Fig, ]. 
Ptyehodera capensis. 
Fig. 2. 
XjF' 
S&Li 
Ptyehodera proliferans. 
transition from one form to the other was observed. The external differences 
between the two" are shown diagrammatically by figs. 1 and 2, in which the 
bright yellow gonads are indicated by stippled shading and the hepatic creca 
by black. Figs. 3 and i represent regenerating fragments, two and four 
weeks respectively after breaking off from the parent. 
As both species are hardy animals, thriving fairly well in captivity when 
supplied with abundant pure sea-water, a number were kept in small glass 
tanks partly filled with sand, and were examined from time to time. The 
