ON THE LIPB-HISTOEY OF PEDIOELLINA. 255 



and generative organs (if these are formed in the primary 

 individual, as is probably the case) and in the complete forma- 

 tion of the vestibular aperture and tentacles. 1 have made no 

 special observations on most of the above points, although on 

 the important question of the origin of the colony from the 

 primary individual, I am able to throw some light. 



In the first place, it may be stated that adult colonies are 

 by no means restricted to one growing point, as stated by 

 Hatschek (1). Of very common occurrence is the develop- 

 ment of two growing points, one at each end of the unbranched 

 stolon : I have noticed this even before the formation of a 

 single secondary calyx. A third growing point may be deve- 

 loped as a lateral branch of the main stolon ; the amount of 

 branching is, however, always slight in P. echinata, and 

 apparently in all cases the oesophagus of each calyx is on the 

 side directed to the growing point to which this calyx properly 

 belongs, as already indicated by Hatschek. 



The formation of the stolon is shown in fig. 13, a longi- 

 tudinal section of the stalk of a completely developed but 

 still solitary individual. The young stolon, which is cut 

 medianly, is developed on the oesophageal side of the Pedicel- 

 lina. The base of the stalk (which is alone represented) con- 

 sists of a thick cuticle, underneath which occurs a layer of 

 ectoderm, surrounding a gelatinous matrix in which lie con- 

 nective-tissue and muscle-cells. The section, however, — an 

 extremely good preparation — is contradictory to the theory of 

 Hatschek, according to which the apex of the stolon is pro- 

 vided with a hypoblastic vesicle derived from the dorsal organ, 

 and engaged in the formation of the mid-gut of the secondary 

 calyces. I may at once state that I have entirely failed to 

 convince myself of the occurrence of any such vesicle, at any 

 period, in the stolon, and I am forced to believe that Hatschek 

 has been mistaken in assuming its existence. Neither in 

 sections nor in entire specimens (whether living or treated 

 with reagents) could I discover the slightest evidence of the 

 presence of Hatschek's vesicle, although I have investigated 

 both adult and young stolons in this connection. 



