ON THK DIPLOOHORDA. 383 



number of embryos adhering to it. The embr\'os usually 

 present a more or less progressive series as regards develop- 

 ment (fig. 20). This band is also found in Ph or on is aus- 

 tralis. 



If we are justified in assuming that the cilia on the inner 

 surface of the tentacles cause a food- and water-current 

 downwards, the water must tend to filter between the tenta- 

 cles into the outer coils, and down them into the median 

 space, where the current would be reinforced by the water 

 directed by the epistome out of the inner coil through the 

 dorsal gap in the tentacles, which I called the branchial 

 fissure This current of water would pour outwards between 

 the two spirals of thelophophore, and over the apertures of the 

 nephridia and the anus. I have not had any live specimens 

 of Phoronis, so cannot demonstrate with certainty that these 

 currents actually exist, but I fail to see any other way of 

 interpreting the structure of the lophophore. This curi-ent 

 would tend to bear away from the animal both the fasces 

 from the anus and the excretory products from the nephridia, 

 but in the breeding season the sexual products would in like 

 manner be carried away from the parent. Whilst this may 

 or may not be a desirable consummation in the case of the 

 spermatozoa, further provision would be necessary to retain 

 the eggs in the lophophore (see figs. 61 and 62). If we 

 may assume that by a contraction of the base of the lopho- 

 phore the openings of the nephridia could be approximated 

 still more to the mouth of the lophophoral gland, the eg*gs 

 would come in contact with the mucus immediatelj^ upon 

 extrusion, and adhering thereto must be carried up the outer 

 coil in the teeth of the down-coming water-current, in which 

 there would doubtless be spermatozoa from another indi- 

 vidual. Sheltered in the tentacles of the parent, the eggs are 

 in this situation not only in the best position for fertilisation, 

 but the continuous stream of water makes the lophophore, 

 like the branchi^ of Lamellibranchs, an ideal "nursery" for 

 the early stages (see fig. 61). 



Again, the fact that the lophophoral glands develop very 



