150 University of California Publications in Zoology, [Vol. 6 



chain may have one, two, or three of these blocks, the number 

 varying with the age of the parent and the size of the zooids. 

 We will refer to the proximal block (B', fig. -t) as the first. 

 The proximal end of this first block is directly continuous with the 

 proliferating stolon, microscopical examination of which is neces- 

 sary to determine the region of transition between the segmented 

 and the nnsegmented parts. The difference in size between the 

 zooids of the first and second blocks is abrupt, especially if there 

 are (inly two blocks in the chain. If there are three, the differ- 

 ence in size between the first and second is slight, but the differ- 

 ence between the second and third is verv marked. 



Fig. 5. — Intermediate piece in a chain of S. fusiformis runcinata: B", 

 second block; B'", thin] block; p", intermediate piece. 



The region of junction between blocks needs special attention. 

 The one between the second and third blocks is shown best in 

 figs. 4 and 5. The sharp distinction between the first zooids of 

 the last block and those of this intermediate region is plainly 

 seen. I call this region the intermediate piece, it not having been 

 given a name by previous writers, so far as I can find. In the 

 specimen figured, which is typical for a long chain, it is apparent 

 that the zooids of this piece not only are much smaller than those 

 of the block, but arc distorted and imperfect. Those at the left 

 in the figure, i.e., toward the proximal end of the chain, merge 

 somewhat gradually into those of the second block. It will also 

 be noticed from the figure that the largest zooids of this second 



