EEPOET ON THE SIPHONOPHOR-ffi. 45 



(PL L. figs. 1, 2) sixteen gonostyles. The medusiform gonophores arise from their 

 proximal part either isolated or in clusters (compare p. 37 above). 



Tentacles. — The corona of submarginal tentacles exhibits in the Discalidse very inter- 

 esting forms, since these organs correspond in the two genera of this family to those of 

 two important larval stages of the Porpitidae. Discalia (PI. XLIX. figs. 1, 4) possesses 

 only eight simple radial tentacles of cylindrical form, which bear no lateral branches, but 

 a simple terminal enidosphere (or a spherical knob composed of radially disposed cnido- 

 cysts). The larva of the other genus, Disconalia, also exhibits in its young state eight 

 simple tentacles (PL L. fig. 9), and hereafter at their distal end a group of four terminal 

 cnidospheres (fig. 10). These become multiplied in older larvae, and form a subumbrellar 

 corona inside the limb of the umbrella. The adult Disconalia (PL L. fig. 1) possesses 

 two rows of tentacles, in which eight perradial bunches are prominent. Each tentacle is 

 cylindrical, with club-shaped distal end, and bears in its distal half three longitudinal rows 

 of pediculate cnidospheres, an odd inferior and two paired lateral series (compare p. 38). 



Ontogeny. — The individual development of the Discalidas is not known, but is probably 

 identical with that of the Porpitidae (compare p. 39). 



Phytogeny. — The phylogenetic value of the Discalidse is, in my opinion, very great. 

 I regard Discalia as a survival of the common ancestral form of all Disconectse, and 

 Disconalia as an intermediate form between this and Porpalia. 



Synopsis of the Genera of Discalidse. 



Umbrella with eight simple tentacles. Pneumatocyst without concentric ring-chambers, . 1. Discalia. 

 Umbrella with numerous tentacles, arranged in eight radial bunches. Pneumatocyst with 



concentric ring-chambers, surrounding the octoradial central disc, . . .2. Disconalia. 



Genus 1. Discalia, 1 Haeckel, \i 



Discalia, Hkl, System der Siphonophoren, p. 29. 



Definition. — Discalidse, with a lenticular or subglobular umbrella, including a lenti- 

 cular pneumatocyst, which is composed of a central chamber and eight surrounding 

 radial chambers, without concentric ring-chambers. Marginal tentacles eight, simple, 

 with a terminal cnidal knob. 



The genus Discalia is the simplest and most primitive form of all Disconectas, and 

 may be regarded as one of the common ancestral forms of this order. It may be com- 

 pared to an octonemal Trachomedusa (Trachynema, Marmanema, Rhopalonema) , which 

 has developed an octoradial pneumatophore in its exumbrella, and in which the eight 

 simple genital sacs of the subumbrella have been replaced by eight palpons or mouthless 

 gonostyles, which afterwards produce medusiform gonophores by budding. 



1 Discalia = marine disc, 8/Woj, aTuoj. 



