W. K. BROOKS ON THE GENUS SALPA. 85 



In Salpa democratica, Plate II, and in most of the species of salpa, it 

 becomes asymmetrical almost as soon as it is recognizable, and it grows 

 around the nucleus in a spiral, as is well shown by Seeliger's excellent 

 figure of the stolon of Salpa democratica (11, Taf. X, Fig. 5), and by his 

 description (11, p. 593), and also in my figure of the solitary form of 

 Salpa africana, Plate IV, Fig. 2, st. 



In Salpa pinnata, Salpa chamissonis, and probably in all the pinnata- 

 like species, the stolon presents a graduated series of stages of develop- 

 ment; each successive salpa, from the root of the stolon to its tip, being a 

 little larger and more developed than the one behind it, as is shown in 

 Plate XLVI, and also in the series of figures on Plates XXIII to XXXIII. 

 In these species the salpa at the tip of the stolon is largest and most 

 developed, and new ones are continually being marked out at the base of 

 the stolon as those at the tip are set free. 



In all the other species the chain-salpae are developed in sets, as is 

 shown in the cut M, and all the individuals in a set are in essentially the 

 same stage, although there is gradation among the members of the 

 youngest set at the root of the stolon. The diagram does not show the 

 number of individuals in each set. They are always very numerous, 

 and in some species each set contains a hundred or more. 



We know nothing of the birth-rate of salpa, but the solitary salpa 

 begins to set free chain-salpae soon after it is born. I have never found a 

 specimen with an exhausted stolon, and there is no evidence of any fixed 

 limit to the process of asexual multiplication. The number of buds on 

 the stolon at one time is very great. Salpa democratica usually has 

 three or four sets at one time, and Leuckart (1, p. 67) found forty in one 

 set and sixty-five in another. Seeliger says (11, p. 593) that he counted 

 sixty-one in a single set in this species, and the average is probably about 

 sixty in each set, or between two hundred and two hundred and fifty in 

 all on the stolon at one time. The stolon of Salpa pinnata has about the 

 same number, from two hundred to two hundred and fifty. The number 

 is very much greater in Salpa cylindrica, and I have counted two hun- 

 dred in a single set from this species. As its stolon carries three or four 

 sets, the total number of buds at one time is from six hundred to eight 

 hundred. 



The position which the bodies of the aggregated salpae occupy when 

 they are first marked out in the stolon has been much misunderstood. I 

 shall show soon that, morphologically, they form only a single series, and 

 that they all arise in exactly the same position, with the neural or dorsal 



