218 Dr. A. Korotneflfow Polyparium ambulans. 



naturally typical, but also is fully in accordance with the 

 requirements of the case. 



Lastly, that the septa of Polyparium are homologous with 

 those of the Actinise may be proved by the production of the 

 new septa. These occur in various stages of development in 

 the intermediate chambers ; they always originate in pairs, 

 and each pair consists of two septa of equal size ; when these 

 are quite small they appear to consist only of a supporting 

 lamella, which is covered on each side with a muscular layer, 

 and it is only after the septa have grown up so as to exceed 

 half the vertical diameter of the colony that the free margin 

 (PI. XIII. fig. 2, s) begins to thicken, forming a pad, and this 

 is the commencement of the formation of a transverse band. 

 Step for step with the growth of the septa proceeds the develop- 

 ment of the muscular pad, and after the septa have reached the 

 buccal surface their amalgamation with the latter ensues, to- 

 gether with the production of a buccal cone, which finally 

 acquires a mouth-opening. The development of the acetabu- 

 lum likewise goes on at the same time. When the septa are 

 still quite small we already observe an annular, scarcely percep- 

 tible fold, which rises more and more and distinctly acquires 

 the form of a knob. Thus it is clear that the growth of 

 Polyparium in length takes place by an interpolation of new 

 members which bear buccal apertures above and acetabula 

 below. 



I must further mention that special orifices occur in the 

 septa, enabling a communication to take place between the 

 interseptal spaces ; these are the so-called internal septal 

 stomata described in the Actiniae. These stomata are oval 

 and have thickened margins closing the aperture, which would 

 indicate the presence of a circular musculature (fig. 3). 



No mesenterial filaments or sexual organs occurred on the 

 septa of Polyparium ; the former are entirely deficient, the 

 latter probably are not developed at the time when I found 

 the animal, that is in the month of September. There can, 

 however, hardly be any doubt that we have to do with a 

 sexually mature organism. In this respect the animal agrees 

 exactly with the Actiniae, in which sexual maturity also occurs 

 only at definite periods. 



in the body of Polyparium we have therefore two systems 

 of muscles, external and internal. The first form two different 

 groups: — 1, transverse muscles, v\hich belong to the ecto- 

 derm, and pass directly from the buccal cones into the buccal 

 disk ; 2, longitudinal muscles, which belong to the entoderm, 

 and run along the whole of the body. The internal muscles 

 may also be divided into two separate groups, both of which 



