MUSEUM OF COMPARATIVE ZOOLOGY. 30 
yet accurately known; we can only form a rough guess from the few ex- 
periments made on the ‘Blake... The lowest point is probably not far 
from 150 fathoms, which is perhaps the limit also of the greater super- 
ficial disturbances of heat, light, and motion, within which we may 
imagine the pelagic fauna to oscillate.” 
I also stated, in 1888 (Am. Jour. of Science, Vol. XXXV. p. 422): 
“ Neither can the method adopted on the ‘ Blake,’ of collecting at inter- 
mediate depths by means of the Sigsbee collecting cylinder, be consid- 
ered decisive. It has not been tried long enough, or frequently enough, 
at great depths (it was not carried beyond 150 fathoms) to decide the 
depth to which the surface pelagic fauna might sink, or to prove the 
existence of an intermediate deep-sea fauna in the depth between 
the surface fauna and the deep-sea fauna.” 
I would also recommend to Haeckel’s notice the following statement, 
by Murray, which is in full accord with the experience of the cruises of 
the “Blake” and of the “Albatross”: “Mr. Murray’s? researches led 
him to conclude that the great majority of pelagic organisms live at 
various depths, down to and even deeper than 100 fathoms, during the 
day-time and rough weather,” and only come to the surface during the 
night and in calm weather.” 
Both Thomson and I were careful to state that the question of the 
bathymetrical range of the pelagic fauna could only be definitely settled 
by the use of tow-nets so constructed as to tow horizontally at inter- 
mediate depths, and capable of being closed at will. 
As for the proposition I enunciated that the deeper parts of the ocean 
contained no org 
Thiere nicht tiefer als 100 Faden hinabgehen” ; that must stand or fall, 
anic life, and not, as Haeckel says, “dass die Pelagische 
or be limited by explorations of a very different character from those of 
the “Challenger.” It is childish for Haeckel to state that the so called 
exact experiments of the “Blake” are absolutely contradicted by the 
positive results of the “Challenger.” If Haeckel is satisfied to base his 
1 Voyage of the “Challenger,” Narrative of the Cruise, p. 218. 
2 Hensen considers the great percentage of water which enters into the composi- 
tion of pelagic animals as a cushion against shocks, while the animals form, as it 
were, part and parcel of the surrounding medium. I may refer here to some meas- 
urements I made regarding the quantity of water entering into the composition of 
Echinoderms and Acalephs, which show how small a percentage of animal tissue 
they contain. For a large Cyanea there was no less than 99 per cent of water. 
The differences in the percentage of water contained in the tissues of pelagic types 
may account for their greater or less sensitiveness to the disturbing influences of 
waves and winds. See Proc. Bost. Soc. Nat. Hist., 1869, Vol. XII. p. 107. 
