REPORT ON THE SIPHONOPHORvE. 215 



or six, in the largest forty to fifty or more. The pedicles of the nectophores are usually 

 small, and easily detached from the axial trunk. 



Pneivmcttophore. — The aeriferous float in all Agalmidse is small, often very small in 

 comparison to the nectophores. It is placed at the top of the trunk, the uppermost part 

 of which is sometimes prolonged, so as to form a contractile pedicle to the float ; in this 

 case it is able either to pass forward over the uppermost nectophores, or at other times to 

 be retracted between them. Usually the float is ovate, spindle-shaped or pyriform. Its 

 top seems to be closed, without a constant opening ; it is often coloured by a small red 

 or brown pigment-spot, and sometimes this forms a regular octoradial star, the centre of 

 which is colourless, like an ocellus. The lower half of the pneumatophore often exhibits 

 a number of equidistant longitudinal ribs, the insertions of the radial vertical septa which 

 connect the outer with the inner wall, and divide the cavity of the pueumatophore into radial 

 pouches ; the number is usually eight, sometimes variable (seven or nine), at other times 

 four, six or twelve ; the upper portion of the septa passes over into the circular muscular 

 ring, which surrounds the pylorus infundibuli like a sphincter or diaphragm. 



Nectophores. — Although the form of the nectocalyces in the numerous Agalmidse is 

 very manifold, it is always developed from the same original type, and represents only 

 variations of a single type, which is defined by their alternately pinnate arrangement 

 on the axial trunk of the biserial nectosome. The quadriradial umbrella of the necto- 

 phores is always bilateral, with a complete symmetry of both its halves. It is more or 

 less depressed in the sagittal direction, from the convex dorsal to the concave ventral 

 side, so that the frontal or transverse axis is longer than the sagittal. The principal 

 axis is sometimes longer, at other times shorter than the frontal; it is directed towards 

 the axial trunk more or less obliquely, and intersects it at a variable angle ; but the 

 apical pole (with the pedicle) is always situated more highly than the basal pole (with 

 the ostium) ; the narrower ostium is directed outwards and downwards. The pedicle of 

 the nectophore, which arises in the median line of its lower or ventral side, is a short 

 triangular lamella ; its proximal apex is inserted on the ventral median line of the axial 

 trunk. This latter is constantly embraced by a pair of large auricles, apical wings or 

 frontal horns, which arise from the dilated lateral parts of the nectophore. The sharp 

 proximal edges of the wedge-shaped horns fit so one over another between the two 

 opposite nectophores, that the axial part of the nectosome in the lateral view exhibits a 

 very characteristic zigzag shape. 



Nectosac. — The subumbrella occupies sometimes scarcely the distal half of the 

 nectophore, at other times its greater part. It exhibits constantly the same bilateral 

 form, with a complete symmetry of both lateral halves, and is depressed in sagittal, 

 dilated in frontal direction. Usually it is divided into three parts, an odd median part 

 with the basal ostium, and two paired lateral parts which correspond to the two frontal 

 horns. The distal ostium is usually small. The four radial canals of the nectosac are 



