THE AXIAL GRADIENTS IN HYDROZOA. 377 



laboratory at variable and generally moderately warm tempera- 

 tures, from 15 to 24 C. (day records). In experiment 6, the 

 pieces were placed in the refrigerator (temp. 13 C.) for the first 

 twelve hours and in experiment n for the first twenty hours 

 after section, and were then removed to laboratory temperature. 

 In experiments 15, 16, and 21 the pieces were kept in the re- 

 frigerator (temp. 13 C.) for the entire period of regeneration 

 as the weather had become unfavorably warm by this time. 

 There was some mortality, particularly among the basal pieces, 

 owing probably to the warm weather. In experiment 6, two 

 basal pieces were living but had not regenerated when the 

 experiment was concluded. In experiment 10, where fifty pairs 

 of pieces were cut, seven basal pieces died and four had failed to 

 regenerate when the experiment was discontinued. In experi- 

 ment 1 1 , three apical halves and twelve basal halves had died or 

 failed to regenerate when the experiment was discontinued. One 

 basal piece died in experiment 21. 



The length of the pieces in all of the experiments recorded in 

 Table III. was 8-12 mm. It was not possible to find stems free 

 from branches long enough to give longer pieces in the summer 

 material, owing to the fact that the colonies are growing rapidly 

 and branching extensively at this season. The number of pieces 

 cut in each experiment depended on the number of healthy stems 

 of sufficient length available in the day's collection. Although 

 material was very abundant and large quantities of it were 

 brought in whenever desired, most of the colonies consisted of 

 stems so short as to be useless for the experiments. 



3. Mass Experiments in December. According to the state- 

 ments of Mr. Gray, head of the supply department at Woods 

 Hole, Tubularia is most abundant and in excellent condition in the 

 early summer reaching a climax in June. After that, as the 

 weather becomes warm, the colonies die away, the protoplasm 

 withdrawing into the perisarc and apparently passing into a 

 dormant state. In the fall, as the water becomes colder, the 

 colonies begin to grow again, reaching their height in November 

 and December, and then with still colder weather, once more 

 passing into the quiescent state, emerging in the spring. In 

 November, 1919, no Tubularia could be found at Woods Hole, 



