174 University of California Publications in Zoology. [Vol- 6 



2. lift ween tlic last two blocks is found a short piece, the 

 intermediate piece, containing imperfect or undeveloped zooids, 

 while in the proximal portion of the chain is a deploying point 

 where the zooids change from single to double file. 



3. A terminal remnant of imperfect zooids is found at the 

 distal end of the chain, unless the distal block is the first ever 

 produced. 



4. The unsegmented chain consists of a tubular sheath of 

 ectoderm enclosing strands containing the various embryonic 

 elements. 



5. The chain elongates ami becomes cut up into a scries of 

 segments, each containing its share of the embryonic elements. 



6. This segmentation is initiated and carried on by the infold- 

 ing of the ectoderm. 



7. As the zooids grow, they push each other out of line so that 

 they change from a single file to double file. 



S. The regular segmentation of the proximal portion of the 

 chain is sometimes interrupted by an unsegmented space. 



9. The blood tubes which run through the chain grow smaller 

 and disappear before the zooids are set free. This disappearance 

 begins at the distal end. 



10. As the vascular connection disappears, papillae develop, 

 which unite adjacent zooids and may or may not furnish nutri- 

 tional connection. 



11. The zooids at the ends of the block are much smaller than 

 the intermediate ones. The maximum size (length or width) is 

 iieai- the distal end in the younger blocks. 



12. In one block of large zooids the maximum size is near. 

 though not at the proximal end of the block. * 



13. In the oldest block, the most proximal zooids are larger 

 than the most distal ones; in the youngest, the distal ones are 

 larger than the proximal. 



14. S. zonaria-cordiformis has no "intermediate piece" or 

 "terminal remnant,*' and the segmentation at the base is not 

 interrupted by an unsegmented portion. The zooids of the blocks 

 are smallest at each end, the maximum occurring near, but not 

 at the distal end. 



15. S. cylindrica has an intermediate piece. The zooids are 



