REPORT ON THE SIPHONOPHOR^. 175 



(superior or abaxial) half than in the rudimentary ventral (inferior or axial) half. The 

 wide opening or ostium of the flat nectosac is sometimes circular, at other times reniform 

 or even cordate, notched by a deep incision in the middle of the ventral margin. Usually 

 two strong ventral teeth (or the lowermost apophyses of the two lateral wings) are 

 prominent over both sides of that notch. 



Canals -of the Nectosac. — The subumbrella of the nectophores possesses in the 

 Polyphyidse, as in all other Siphonophorse, four radial canals, united by a marginal ring- 

 canal above the velum. But they are here peculiarly differentiated. The pedicular 

 canal of each nectophore, which arises from the tubular stem and runs through the 

 lamellar pedicle, is short and divides in the middle of the ventral groove into two 

 branches, an ascending and a descending. The ascending branch is a simple blind 

 pallial vessel (corresponding to the superior mantle-canal of Pray a) ; it runs in a radial 

 direction, inside the jelly-mass of the nectophore, towards its outermost and uppermost 

 dorsal angle (between the median line of the ventral groove and the dorsal side of the 

 nectosac). The descending branch runs to the top of the subumbrellar cavity, and 

 divides here into four very unequal branches or radial canals. The median dorsal and the 

 two paired lateral canals are very short, and soon open into the marginal canal. The 

 median ventral canal, however, is very long and dilated towards the margin of the 

 umbrella ; it forms here a flat sinus or diverticulum, the form of which is very 

 characteristic of the individual species (sinus ventralis, cv", figs. 3. 4, 13, 14). It is 

 elliptical or ovate in Hippopodius gleba, hexagonal in Polyphyes ungulata, two-winged 

 in Vogtia kbllikeri, &c. The cells of the entoderm, which line the flat and broad cavity 

 of this ventral sinus, are very large, polygonal, and filled with peculiar fine granules. 

 The narrow intervals between the single cells have been described by Claus as " peculiar 

 ramifications of the vessel" (35, p. 553). 



Siphosome (fig. 1). — In the Polyphyidae the trunk of the siphosome, or the common 

 stem which bears the cormidia, is usually contracted and retracted into the hydrcecial 

 cavity of the nectosome. But in the expanded state, and protruded through the basal 

 opening of that cavity, it is a rather long tubular stem, two, three, or more times as long 

 as the nectosome. The number of cormidia is sometimes small, four to eight, at other 

 times much larger, twenty to thirty or more ; besides the numerous buds of young 

 cormidia, which are found in a crowded ventral series along the uppermost part of the 

 siphosome (PL XXIX. fig. 7, is). 



Cormidia. — The groups of polymorphous persons, which cover the trunk of the 

 siphosome, differ from those of all other polygastric Calyconectse in the complete absence 

 of bracts. This may be explained either by total reduction and loss of the hydrophyllia 

 (perhaps in correlation with the development of the large nectosome and its peculiar 

 hydrcecial cavity), or by a phylogenetic dislocation of organs which were originally 

 connected. It is possible, that in older ancestral forms of this family, the 



