The volume range calculated as a prolate spheroid was 

 determined by adding and then subtracting the ocular micro- 

 meter error from the values obtained. 



The low ratio averages for Groups I and II (table 2, 

 column 10), 1. 07 and 1. 02, respectively, suggest that the 

 internal pressures of float gases are virtually at ambient, 

 and that any variations which appear are due to the errors 

 described, and possibly to the degree of deviation of the 

 shape of the gas phase from the ideal prolate spheroid. 



The fact that the floats in Group I are more homo- 

 geneous in respect to size than those of Group II (table 2, 

 column 6) is possibly an indication that our net when col- 

 lecting Group II was sampling from two more or less dis- 

 tinct age groups or sublayers of the DSL. This is possibly 

 due to vertical cycling behavior of the net as shown in char- 

 acteristic depth records (fig. 8). The cycling was due to 

 the inability of the towing vessel to maintain a constant 

 slow speed (i.e., less than about 3 to 4 knots), thus neces- 

 sitating continuous engaging and disengaging of the ship's 

 clutch. 



Barham 3 has observed from the bathyscaph as many 

 as three distinct siphonophore layers associated with sonic 

 scattering, each made up of siphonophores of different size 

 and presumably, therefore, of different age. 



It is of interest to compare volume observations 

 made upon specimens of Rhtzophysa sp. This siphonophore 

 possesses a pneumatophore some 30 to 40 times the volume 

 of Nanomta, but lacks nectophores (swimming bells). Pro- 

 pulsion presumably is supplied by controlling gas volume 

 by means of an apical pore, and by contraction of the com- 

 paratively short stolon. This species is probably capable 

 of expelling gas by constricting the float as shown in figure 

 3, but does not appear to possess longitudinal septa in the 

 float walls as do nanomians. It is not known at the present 

 time how many of these interesting siphonophores are pre- 

 sent in the San Diego Trough area, and although the float is 

 certainly an excellent acoustic target, thus far this species 

 has seldom been captured in net hauls made through zones 

 of sonic scattering in this area. * 



* Abundant individuals of Rhizophysa filitormis have been sighted during bathyscaph 

 dives in the Mediterranean, however. See reference 10. 



19 



