62 



EMBRYOLOGY 



nutritive polyp, polypite, is developed from the latter by 

 the breaking through of a mouth-opening at the lower pole. 



Thus a larval form is reached in Halistemma pictum, which recurs 

 frequently among the Physophoridse, and consists of the apical pneumato- 

 cyst and a polypite with accompanying tentacle. In it we recognize the 

 Auronectid larva described byHAECKEL (No. 70), and referred to Stephalia 

 corona, which, in addition to the extensive pneumatophore, also exhibits 

 the fundament of the remarkable apparatus for the elimination of air 

 (aurophore). Moreover, it appears to occur among the Pneumatophoridae 

 (Chun). Thus the youngest Physalid larvae, which have been made 

 known through Huxley and Haeckel (No. 70), are constructed after this 

 type (Fig. 25). Not until a later period do the air-sac, which increases 

 considerably in size, and the rudiment of the stem, assume a more 

 horizontal position, whereby the formerly apical pore of the pneumato- 



FiG. 25.— Youngest larval stage of a Physalid (Alophota Giltschiand) (after 

 Ha£Ckel). p, pneumatophore; po, its apical stigma; a, rudiment of the stem; 

 m, polypite ; /, tentacle. 



cyst comes to occupy the anterior end, the insertion of the primary 

 polypite, on the contrary, the posterior end. of the body, on the under 

 (ventral) side of which new groups of individuals (polypites, dactylo- 

 zooids, with tentacles and gonophores) now bud forth. Later the so- 

 called pneumatic plate is developed on the inner side of the air-sac 

 (modified pneumatic funnel), and also the dorsal comb (Chun, No. 58). 



The development of Halistemma rubrum takes place, according to 

 Metschnikoff (No. 13), in a similar way to that of H. pictum, differing 

 from it principally in the early appearance of the buds of the nectosome 

 [Schwimnutdule], which are developed on the ventral side between the 

 fundament of the pneumatophore and the first tentacle. The first 

 nectocalyx bud isestabhshed very early, at the same time as the pneumato- 



