156 . T. H. MORGAN. 



covered with sand or were thrust into little heaps of sand no oral 

 stolons developed. 



Influence of Diluted Sea Water. 



Some observations of C. D. Snyder on Tubularia crocea of the 

 Pacific Coast seemed to him to indicate that in dilute sea water 

 more basal polyps are produced than in normal sea water. In 

 several experiments that I made with T. crocea of Woods Hole 

 in which the sea water was diluted no more basal polyps developed 

 than in the control in sea water. The occurrence of basal polyps 

 is so variable that only a thoroughly controlled set of experi- 

 ments would suffice to prove that dilution affects basal polyp 

 formation. 



Direction of Currents. 



In Tubularia a current passes up one side of the hollow stem 

 and down the opposite side. When more than one dissepiment 

 is present there may be two currents in one direction and one or 

 two in the reverse direction. Those who maintain (Goebel and 

 Loeb, for example) that currents may determine polarity might 

 hope to find in the direction of these currents in Tubularia a 

 solution of the problem of polarity. In fact Loeb has sugges- 

 ted such an hypothesis. Since however there is a current in each 

 direction it is difficult to understand how this idea could be sup- 

 posed to account for the difference in the behavior of the two 

 ends, unless indeed there is a dorsal and a ventral side to Tubu- 

 laria (which seems to be radially symmetrical) so that the dorsal 

 side of the oral polyp is on the opposite side from that of the 

 basal polyp. This supposition is not however in harmony with 

 the heteromorphosis in other forms, such as the earthworm or 

 planarians. In these the ventral and dorsal surfaces are the 

 same in the old and in the heteromorphic structures. The only 

 alternative would be to expect, if the currents in Tubularia 

 are a factor in the direction of regeneration, to find that the 

 current near the basal, or heteromorphic polyp is reversed in 

 direction as compared with that going to the oral polyp. 



I have examined the direction of the current in a number of 

 long double pieces, and have found that the direction is continuous 

 along each half of the piece and not different at the two ends. 



