1910] Johnson: Quantitativi Study of Salpa Chain. liil 



In series XI-XH, the vascular connection was evidently lost 

 throughout the greater part of the block and about two inches 

 of the chain protrude from the body of the parent. It is im- 

 portant tn know when the zooids begin to take nourishment from 

 external sources on their own account. The oral openings seem 

 to he complete in all the chains that have been measured, hut 

 it is doubtful if nourishment is taken until the zooids have 

 been set free. Examination of the digestive tract of some of the 

 larger zooids indicates that nothing has been taken in this way. 

 In the parent salpae, the intestines are always well filled, so that 

 if the zooids have taken food we should reasonably expect to find 

 some trace of it in the digestive tract. It is possible that the 

 cleft in the test through which the block is discharged does not 

 entirely close after a block is set free and that the water may 

 have access to the cavity in which the developing block lies, thus 

 bringing nourishment to the zooids before they leave the parent. 



A question naturally arises concerning the comparative sizes 

 of the newly formed segments of the first block. Is there a 

 difference corresponding to the difference in the progressive seg- 

 mentation, or is the block the same size throughout? So far as I 

 can tell, there is no measurable difference in the diameter of 

 different parts of this block. However, there is a slight con- 

 striction at the point where it passes into the second block and 

 sometimes just in front of the stolon. Even in the stage of the 

 second block in fig. 4, there is no measurable difference in the 

 diameter at different points except in the few zooids at the ends. 

 Therefore, the differences in size arise mostly with the later 

 growth of individual zooids. At the same time, it must be 

 remembered that these younger blocks are but little more than 

 flimsy hollow tubes which are curved and sometimes twisted and 

 very difficult to measure. 



5. SALPA ZONARIA-CORDIFORMIS. 



A brief examination of specimens of Salpa zonaria-cordi- 

 formis was made for comparison with those of fusiformis- 

 runcinata. The chain in this case arises in the ventral median 

 line about 0.5 cm. anterior to the nucleus, and extends posteriorly 

 and to the right almost as far as the nucleus. Here it bends 



