REPORT ON THE SIPHONOPHORiE. 99 



two or three gonophores are developed simultaneously in a single cormidium, and in 

 some genera (IAlyopsis, Desmophyes) a bunch of numerous clustered gonophores ; then 

 usually their umbrella is more or less rudimentary, whilst still a " special nectophore " 

 is developed as a swimming organ. 



Each single gonophore is always gonochoristic, either male or female. Those cor- 

 midia, which bear two or more gonophores, are usually also gonochoristic (diclinic) ; but 

 in some cases they are hermaphrodite, one of the gonophores being female, the other 

 male (monoclinic cormidia). The corms of the polygastric Calyconectse are usually 

 monoecious and bear cormidia of both sexes, sometimes regularly alternating (as in 

 Cymbonectes, PL XXVIL, and Desmophyes, PL XXX.). At other times the distal 

 (older) cormidia are males, and the proximal (younger) cormidia females. A few genera 

 of polygastric Calyconectse are dioecious, each cormus bearing only gonophores of one 

 sex, either male or female (Mitrophyes, Galeolaria). But the question of the relation 

 of these different forms of sexual differentiation requires a further examination. 



Umbrella of the Gonophores. — The calyx or umbrella of the sexual persons has in 

 all Calyconectse the same structure as in a common simple quadriradial Hydromedusa. 

 Its form is very rarely quite regular, hemispherical (as in Diplophysa and some Poly- 

 phyidae) ; usually it is more or less bilaterally symmetrical, in adaptation to its place 

 inside the bracteal cavity, at the ventral side of the siphon ; sometimes it is strongly 

 asymmetrical, as in Amphiroa (PL XXXVI. figs. 12-25) ; here two gonophores are 

 developed simultaneously on each side of the siphon (right and left) ; each corre- 

 sponding to an antimere, so that the two together form a symmetrical pair. 



The Exumbrella of the Gonophores corresponds in its general form to a certain degree 

 with that of the nectophores. It' is therefore evenly convex and smooth, without pro- 

 minent edges, in most Sphseronectarise (Sphseronectidse, Prayidse, Hippopodidse). On 

 the other side, it is quadrangular, pyramidal, or prismatic, in most Cymbonectarise 

 (Cymbonectidaa, Diphyopsidse, Abylidae). Usually in the latter the four edges of the 

 exumbrella are sharp and prominent, often elegantly denticulate, and wing-like dilated in 

 the distal part ; their distal ends are often prominent as four strong triangular teeth over 

 the basal ostium of the umbrella. Often two paired dorsal edges and their terminal 

 teeth are much more developed than the opposite two ventral edges. More rarely a 

 single wing is stronger than the three others, or even five wings may be developed 

 instead of four (compare Amphiroa, PL XXXVI.). The uppermost part of the exum- 

 brella is usually prolonged into an apical horn, or a hook-shaped apophysis, which 

 serves for its insertion into the bracteal cavity. 



The Subumbrella of the Gonophores has always a well-developed layer of ring-muscles 

 (iv), and, on its distal prolongation, a circular velum (v) which closes the peripheral part 

 of the opening of the subumbrellar cavity. Four radial canals (cr) always run in the 

 subumbrella from its apex, diverging to its basal ostium, where they are united, above 



