1! ""l Johnson: Quantitativt Study of Salpa ('hum. 



151 



block are those which are a shorl distance from the end, not those 

 next to the intermediate piece. The region between the first and 

 second blocks, I will call the "deploying point." (p', fig. 4.) It 

 is different in structure from the intermediate piece and will be 

 understood better after the development of the chain is described. 

 When the terminal block of the chain is not the first one 

 produced by the parent, others having been thrown off, there is 

 present at the distal end a number of small, abortive zooids. It 

 seems probable that these zooids are the remnant of what would 

 be an intermediate piece if a fourth block were present. If one 

 removes a large block from the chain, the separation occurs at 

 the first zooid of the block, leaving the entire intermediate piece 

 as the terminal remnant of the block that remains. 



Pig. 6.— Cross-section through tlie first -block of a chain of S. fusiformis 

 runcinata. 



Examination of a eross-section close to the proliferating 

 stolon (Fig-. 6) shows it to consist of a tubular sheath of ecto- 

 derm e, a nerve tube ii. an entodcrmal tube en, two peritho- 

 racic tubes pi and pf, two blood tubes I and t' ami a genital rod 

 g. These run throughout the chain, their relative positions 

 usually remaining the same as far as the deploying point. 



As the development in Salpa fusiformis-runcinata, so far as I 

 have examined it. agrees in most respects with what Brooks 



