120 Dr. M. Ussow on a neio 



divides into two B^. The proboscis with the buccal aperture 

 takes part in all these halvings, the buccal fissure being 

 halved by longitudinal partitions (walls of the proboscis 

 itself). 



The radial tentacles serve our animals chiefly for locomotion 

 and for grasping, whilst the feelers may rather be regarded 

 as offensive and defensive weapons. Jointly they support the 

 body in the resting state upon the bottom of the vessel, so as 

 to produce an appearance as if it stood upon stilts, when the 

 proboscis with the buccal aperture is placed at a considerable 

 distance (5-6 millim.) above the bottom (fig. 11). From 

 time to time one or other of the tentacles bends, bringing its 

 extremity to the buccal aperture, when the lips, by very 

 appropriate movements, strip off the mucus and with it spores 

 and other micro-organisms (Infusoria, and frequently also 

 Eotatoria) stupefied by the urticating elements. In the forms 

 B and B^ the coordination of the movements to one another 

 upon the opposite sides of tlie body is generally well marked and 

 the equilibrium is lost (thus, perhaps, favouring the separation 

 of the halves of the body), especially upon external irritation, 

 only during the process of division into two new individuals. 



Without entering here into a detailed description of the 

 histological structure of the free-living generations, I will at 

 present only remark briefly as follows : — 



1. The ectoderm appears more strongly folded on the sides 

 and lower part of the body ; between the ectodermal elements 

 rather elongated cells are to be observed, which are produced 

 into capillary bacilli projecting beyond the surface of the 

 ectoderm. To all appearance we have here to do with sense- 

 cells ; they are met with most numerously at the inferior 

 furrows. 



At each side of the buccal aperture two rounded cell-aggre- 

 gations are observed in the proboscis at its passage into the 

 body, consisting of larger elements than the ectodermal cells. 

 Their structure, I think, justifies our interpreting them as 

 ganglia. Whether nerves are also present, perhaps forming 

 an oesophageal ring, is unknown to me at present. After 

 living freely for two or three days, and the complete assimi- 

 lation of the yolk- mass contained in its interior, the body of 

 the Polyjjodium acquires a light greenish colour, due to 

 pigment-granules which are suspended in the protoplasm of 

 the ectodermal cells. 



2. The endoderm likewise forms an enlargement at the 

 aboral end of the body at the sides of the transverse furrows 

 (especially in the mother-form B). In the region of the 

 proboscis also there is a small annular fold, which projects 



