'74 G. M. Giles — On tlic Protliallas of Padina pavonia. [No. 2^ 



tube structure, can hardly fail to be brought into actual contact by the 

 gentle osmotic currents which must always be in progress in such a 

 structure as this. 



This suposition is strengthened by the fact that young Padina 

 fronds appear always to spring up, not in the neighbourhood of, but 

 actually from the substance of the decaying prothallus. There can be 

 little doubt, then, that the two kinds of tubular body are respectively 

 of the nature of antheridia and archegonia. The rod-shaped produce of 

 the smaller form make its antheridial nature little doubtful, and the 

 produce of the larger kind is so much like the spores produced by directly 

 sexual sea- weeds that there can, I think, be equally little doubt as to 

 the -rdZe to be assigned to them. 



There remain to be described the peculiar opaque bodies previously 

 noted, and as to their nature no such relative certainty can be felt. 



The surmise to which one feels most naturally led, is that they may 

 be the fertilized spores in an early stage of development. They are, 

 however, like nothing I have met with elsewhere either amongst algae or 

 in animal or vegetable histology. The bodies in question (Figs. 7 and 8) 

 lie loose in the meshes of the adenif orm tissue of the white peripheral layer 

 of the prothallus. They are from 15 to 25 m. in diameter and of 

 generally spherical form. In their fully developed form they appear to 

 consist of one or more layers of minute colourless rods radiating from a 

 common centre, so that their entire periphery is beset with minute blunt 

 spines, on which account I have named them hedgehog cells. Inter- 

 mediate stages can be traced between these and cells closely resembling 

 the " spores " of the contents of the larger form of tubular body. They 

 are quite white when seen by direct illumination, while their opacity 

 renders them quite black when examined by transmitted light. They 

 are confined to the under surface of the prothallus, where it comes 

 in contact with the rock and are there very abundant ; the lateral 

 and upper parts of the peripheral layer of the thallus being composed 

 of the adenif orm tissue without any such contents. 



The parts of the central substance between the groups of tubular 

 bodies is filled up with very loose adeniform tissue enclosing in its 

 meshes immense numbers of spherical cells containing abundant chloro- 

 phyll. These are from 12 to 15 m. in character, and probably fulfil a 

 nutritive function. 



The curious resemblance of the tube-bodies to an ovo-testis can 

 scarcely be missed, and more than once caused me to reflect whether or 

 not the structure might by any possibility be of animal origin. Repeated 

 examinations, however, have assured me that this is not the case and 

 that the body in question is an intermediate stage of the sea- weed in 



