Dr. A. Korotneff on Poljparium ambulans. 205 



this latter cylindrical margin, as also along the whole back of 

 the colonj, are placed conical, chimney-like tubercles (buccal 

 cones, as we shall see hereafter), which are rather scantily 

 distributed, but become more and more crowded together 

 towards the bordered margin, along which they form a regular 

 palissade. 



Counted transversely the number of the buccal cones is 

 from four to six ; in the longitudinal direction we do not 

 recognize any serial arrangement of them, and they show no 

 particular regularity. The breadth of each cone at the 

 base is 1 millim. ; the height varies according to the state in 

 which the buccal cones may happen to be ; when con- 

 tracted they are not more than 1 millim., but when drawn 

 out they measure twice as much. At the apical pole of each 

 mouth-tubercle there is an aperture. But the most remark- 

 able thing is their entire want of tentacles ; neither the margin 

 of the aperture itself nor its vicinity bears tentacles or any 

 structures which might be homologous with tentacles. 



The inferior surface by which the colony adheres to various 

 objects (fig. 1) is, as already stated, covered with acetabula, 

 and further traversed by two furrows running along the whole 

 colony in such a way that we can distinguish an intermediate 

 area and two lateral streaks ; the median area is twice as 

 broad as the lateral streaks, and of the latter the one the 

 margin of which is bordered is band-like, while the other, 

 without a border, is rounded off and passes directly into the 

 dorsal surface. The median area, in a transverse direction, 

 has from two to four rows of acetabula, the lateral streaks 

 only two. The position of the acetabula seems not to be 

 regular, although in certain parts of the sole they appear to 

 be arranged in longitudinal rows ; perhaps the appearance 

 observed after the death of the animal may be due to processes 

 of contraction. The interspaces between the acetabula are 

 not quite flat, but they possess transverse folds which^ in the 

 living colony, are scarcely noticeable, but make their appear- 

 ance rather strongly after the action of alcohol. 



As regards the individual acetabula, each of them forms a 

 button -8 milHm. in breadth, with a flattened, somewhat 

 notched surface. The size of the acetabula varies very con- 

 siderably. 



The internal structure of Poli/parium is not less singular 

 than its exterior. The best mode of acquiring a knowledge 

 of the internal organization consists in cutting a piece out of 

 the whole colony by transverse sections, and then dividing 

 this into vertical sections parallel to the longitudinal axis ; 

 sections made in other directions are not particularly instruc- 



