256 Uniuersitij of California Fublicatious in Zoology [Vol. 18 



abundance occurring with maximum frequency and also with the colder water 



1-P 

 in any one tabulation (as is the case with the solitary forms) would be • 



Hence, the probability of maximum abundance and frequency of aggregate 



forms being associated with minimum abundance and maximum frequency of 



p /l-P\ 

 the solitary forms and with the colder water m any one tabluation is - I --^ I or 



p.pz /P-P=\' 



, and the probability of this happening three times in succession is I 1 



(p.p-v3 

 — — 1 = YiG^, and 



since this is the value P assumes if abundance be independent of frequency, 

 it follows that the probability would be less than Yiq^ if a natural association 

 exists between maximum abundance and maximum frequency. Furthermore, 

 the magnitudes of the differences between maximum and minimum abundance 

 and between maximum and minimum frequency, as well as the number of hauls, 

 have not been considered, so that the probability 0.0007 must be regarded as 

 a large overestimate rather than an underestimate. 



It therefore follows that the odds in favor of the trustworthiness 

 of the relations shown by tables 4, 5, and 6 are sufficiently large (more 

 than 1,535 to 1) to justify the conclusion that temperature, or some 

 influence intimately associated with it, must play a prominent, albeit 

 a peculiar, part in the distribution of Salpa democratica. 



2. A Morphological Implication 



What do the foregoing facts imply? Since solitary forms accumu- 

 late on the surface in greatest numbers when the water is warm, while 

 aggregate forms accumulate in greatest numbers when the water is 

 cold, some definite relation must exist between them, compelling soli- 

 tary forms to be taken in cold water w^henever aggregate forms are 

 captured, compelling aggregate forms to be taken in warm water 

 whenever solitary forms are captured, and preventing any of one 

 generation to be taken without some of the other. Were there no such 

 relation, I can conceive of no way in which the two generations could 

 be so nearly identical in frequency and at the same time reversed in 

 abundance. 



Upon considering the life cycle, two possible relations are sug- 

 gested : ( 1 ) that individuals of the solitary generation are developed 

 until maturity within the body of those of the aggregate generation 

 (p. 245) ; and (2) that the aggregate salpae are budded off in the form 

 of a chain by the proliferating stolon of the solitary salpa (p. 243). 

 The first alternative might account for the capture of at least one 

 solitary form in cold water by each haul that captured a number of 



