REPORT ON THE SIPHONOPHOR^E. 97 



series of lateral branches or tentilla. Each tentillum is a thinner cylindrical tubule, and 

 is constantly composed of three different parts — (1) a thin pedicle or proximal portion 

 (tp), (2) an inflated cnidosac as a dilated middle part (tk), and (3) a thin distal portion, the 

 terminal filament (tf). The closed distal end of the latter is sometimes vesicular ; so 

 also the distal end of the pedicle is sometimes club-shaped. The structure of the thin 

 cylindrical pedicle and of the long terminal filament is simple and always the same, 

 whilst the cnidosac, placed between them, exhibits a complicated, and more or less varied 

 structure (compare PL XXVII. fig. 7; PL XXVIIL fig. 8; PL XXXII. figs. 12-14; 

 PL XXXIV. fig. 18 ; PL XXXVI. fig. 26 ; PL XXXVIII. fig. 16 ; PL XL. figs. 19, 20). 



The cnidosac (or sacculus) of all CalyconectaB is originally nothing more than an 

 inflated dilatation of the middle part of the simple cylindrical tubular tentillum. This 

 dilatation seems to be produced by the stronger development of larger cnidocysts on one 

 side of its middle part. This side, which contains the so-called " cnido-battery," is the 

 convex dorsal side of the cnidosac, whilst the opposite ventral side is usually more or less 

 coneave ; it contains two parallel elastic bands, which seem to form together a noose at 

 the distal end of the cnidosac, the so-called " cnido-band or angle-band." The whole 

 cnidosac, therefore, has a bilateral form, usually more or less ovate, pyriform, or kidney- 

 shapecL In most Calyconectae it is more or less compressed from both sides, so that the 

 sagittal axis is larger than the frontal, but smaller than the principal axis. 



The differentiated cnidocysts, or thread-cells, which are crowded in great numbers in 

 the '• cnido-battery " at the convex dorsal side of the cnidosac, occur generally (probably 

 in all Calyconectse) in three different forms — (l) very numerous, small, and palisade- 

 shaped (paliformes) ; (2) few, large, and sabre-shaped (ensiformes) ; (3) small and pear- 

 shaped, in a distal group (pyriformes). These are so arranged that several parallel rows of 

 paliform or medial cnidocysts occupy the whole convex dorsal side of the cnidosac [km), 

 two bilateral groups of a few large ensiform cnidocysts are placed at each side of its 

 proximal basal part (kg), and an odd distal group of small pyriform cnidocysts (kp) lies 

 at its distal end, at the base of the terminal filament (tf). 



The small palisade-shaped or medial thread-cells (Cnidocystse paliformis, km) are 

 always very numerous, usually some hundreds in number, and comprise far the greatest 

 part of the crescentic cnido-battery, occupying the dorsal half of the sacculus. They 

 are arranged so regularly that they form together a certain number (usually four, six, or 

 eight) of parallel longitudinal columns, each composed of a single series of numerous (twenty 

 to fifty, or more) cnidocysts. All the latter are cylindrical or spindle-shaped bacilli, of 

 similar form and equal size, three to six times as long as broad, sometimes straight, at 

 other times slightly curved. Their axis is perpendicular to that of the sacculus. The 

 convex dorsal surface of the sacculus, therefore, appears elegantly panelled or facetted, 

 the outer or abaxial ends of the paliform cnidocysts forming regular transverse rows 

 (crossing the longitudinal rows). 



(ZOOL. CHALL. EXP. PART LXXV1I. — 1888.) Hhhh 13 



