166 I'liin rsity of California Publications in Zoology. [Vol. 6 



7. DISCUSSION OP RESULTS. 

 In considering these developing salpa chains, the question 

 immediately suggests itself, what does the division into blocks 

 signify? 



Classifying the stages of development of the whole chain, 

 their outward manifestations fall into certain phases; first, the 

 growth of the unsegmented stolon; second, segmentation of this 

 stolon; third, growth of the individual zooids resulting in the 

 formation of blocks; fourth, the final separation of the block of 

 /.oiiids from the rest of the chain. 



What is the relation between these four phases, which are so 

 balanced thai there are always present in the chain at least two 

 blocks? Does the growth of the zooids and shifting of position 

 at the deploying point go on at the same rate as the segmentation 

 and outgrowth of the stolon ? If the latter processes are con- 

 tinuous would not the former be so also, and why should the 

 abrupt break at the intermediate piece occur? In other words, 

 if growth of the stolon, segmentation, and development of the 

 zooids are continuous, how does the discontinuity represented In- 

 die intermediate piece and blocks arise and what is the cause of it ? 

 If we could keep the parent salpae alive and watch the 

 development of the chain, we could easily see how development 

 proceeds, but the animals are so sensitive to the artificial con- 

 ditions of the aquarium that this has not yet been found possible. 

 We must for the present depend upon our observations on the 

 preserved material for such answers as we may get to our 

 questions. 



The differences in the condition of the early segmentation are 

 suggestive. It will be remembered that in S. fusiformis-runcinata 

 a break in the continuity of segments sometimes occurs. The 

 division planes almost or quite disappear for a short distance 

 and reappear beyond, being again gradually lost nearer the root 

 of the stolon. (Fig. 8.) Again, some blocks do not appear to 

 have this break, the division planes being only lost gradually at 

 the root of the stolon. The latter condition is also found in 

 S. cylindrica. It will be remembered that the chain of both these 

 species has an intermediate piece consisting of rudimentary 

 zooids between the two largest blocks. 



