266 TJuivcrsiti) of California Publications in Zoology I Vol. 18 



cession, it is difficult to see how solitary forms could by this means 

 predominate in the warm areas without also involving a predominance 

 of aggregate forms in the same areas. For, as stated on page 245, each 

 individual of the aggregate generation can give birth to but a single 

 solitary form and then not until the stolon of the latter has begun 

 to be converted into salpae of the next generation. This makes it neces- 

 sary, as in the case just considered, for all hauls obtaining an excess 

 of solitary forms over aggregate forms to have been made during that 

 brief and improbable time interval in the life cycle between the pre- 

 mature death of many of the embryo-bearing salpae and protrusion 

 of the first salpae of the next generation from the mantle cavity of 

 the solitary form. 



But, assuming the hauls to have been made in this improbable if 

 not impossible manner, the verity of the hypothesis hinges upon 

 whether or not stratified areas of warm and cold surface water per- 

 sisted for a sufficient length of time. In other words, were the major- 

 ity of Avarm water hauls made at one set of positions and the majority 

 of cold water hauls at another set ? If so the above hypothesis might 

 be true ; if not it is obviously inadequate. 



To answer this question the following list is supplied, which gives 

 the distribution of hauls involved in table 4 with respect to position, 

 the unit of position being a rectangular area or section of five miles ( or 

 more accurately five minutes), on a side. In designating the section, 

 the mimber denotes its distance in five-minute units west of 114°'W, 

 while the suhscript denotes its distance in five minute units north of 

 32°N. For further explanation see Michael and McEwen (1915, 

 p. 46; 1916, p. 217) and McEwen (1916, pis. 1-3). 



List Showing Distribution op Hauls Involved in Table 4 by Sections 

 Number of hauls in Number of hauls in 



