1910] 



Johnson: Quantitativi Study of Salpa Chain. 



14!) 



posterior three being confluent on the dorsal side. Pig. 2 shows 

 the free swimming or fully developed zooid, while the younger 

 one shown in fig. 3 was detached from the chain. It is thus seen 

 that the individuals of the two generations are very different in 

 structure as well as in mode of origin. 



3. MORPHOLOGICAL OBSERVATIONS. 



The main problem in the investigation has been, as stated, the 



quantitative relation of the developing zooids, but it has also 



been found necessary to give some attention to certain questions 



of structure and function which affect the final results. These 



Fig. 4.— Portion of chain of 8. fusiformis runcinata: B', first block- 

 fie'ce SeCOml bl0Ck; B '"' third b '° Ck; P '' de P Io y in g P° int ; P"> intermediate 



are chiefly, the manner of segmentation of the chain, the arrange- 

 ment of the zooids. and their mode of nutrition at various stages 

 in development. 



The chain originates in the median line, just anterior to the 

 "nucleus." (Pig. 1.) It extends toward the oral extremity 

 for a few mm. and then bends to the left, encircling the nucleus 

 so that the distal end of a well-developed chain is found at the 

 right of the nucleus, the chain reaching three-fourths of the way 

 around. 



The zooids of the chain, instead of being in an evenly gradu- 

 ated series, the least developed at the proximal and the more 

 mature at the distal end, are arranged in groups, or blocks (fig. 

 4i. those of each block being approximately the same size. The 



