JOUSSEAUMIA. 247 



the youngest forms, I suspect that these may escape from the Aspidosiphon chamber 

 and use the foot for progression and for springing on and attaching themselves to an 

 Aspidosiphon when projected from the basal aperture of another coral. At all events, 

 there must be some means by which Jousseaumia can be transferred from coral to 

 coral, and the highly developed musculature of the geniculate foot suggests that the 

 transference is effected in this manner. The anterior and posterior retractors of the 

 foot are well developed and together form an elongated muscular band, by which 

 the foot appears to be slung up in the mantle cavity. Practically the whole of 

 the viscera are dorsal to this band. The protractor muscle of the foot is also well 

 developed and has a separate muscular slip ventral to the anterior adductor muscle, 

 and it is evident that, in spite of its sedentary habit, Jousseaumia shows no 

 degeneration in the organs of progression. 



The attachment of the young forms to an Aspidosiphon inhabiting another coral 

 would be effected by means of the byssus, which has the form of a moderately stout 

 thread, branching and ending distally in adhesive enlargements. The posterior edge 

 of the foot is furrowed by a well-marked byssus groove leading into a byssus cavity 

 at the hinder end of the foot. As the structure of the byssus gland and the mode of 

 formation of the byssus has been a subject of dispute, and as some of my specimens 

 were sufficiently well preserved to enable me to make tolerably accurate observations, 

 I shall describe the histology of this organ in some detail. The whole of the centre 

 of the foot is occupied by a core of more or less polygonal relatively large glandular 

 cells which appear pale in sections stained with borax-carmine and picro-indigo- 

 carmine, but stain deeply in hsematoxylin or safranin. With the last-named dye the 

 gland cells stain brilliant scarlet, and the stain is shown by high powers of the 

 microscope to be confined to minute granules with which the cells are stuffed. The 

 behaviour of these cells and granules will be described later. The byssus groove 

 begins as a very shallow furrow near the pointed extremity of the foot, and gradually 

 deepens as it passes dorsally along the posterior edge of the foot, eventually ending in 

 a duct which enlarges to form a considerable byssus cavity contained in the upper 

 part of that organ. Fig. 4 is a section taken through the open part of the groove 

 near the middle of the foot. It shows the structure described by CARRI^RE (5) and 

 HORST (8), namely, a furrow of irregular shape opening to the exterior, and in the 

 depth of the furrow a crescentic gutter or demi-canal (" halbmondfdrmige Einne") 

 bounded on either side by a projecting fold. Contrary to the statements of previous 

 authors, I find in Jousseaumia that the furrow is lined by a low, non-ciliated 

 epithelium continuous with that of the external surface of the foot. This epithelium 

 has a distinct cuticle, staining blue in picro-nigrosin or picro-indigo-carmine, and 

 though I am unwilling to make a positive assertion in consequence of the indifferent 

 state of preservation of my specimens, I can say that I was unable to find any trace 

 of cilia either in the furrow or on the external surface of the foot. The crescentic 

 demi-canal, on the other hand, is lined by larger cubical or short columnar cells, with 



