236
explaiiatiou of this second change which Avas first
suggested hy Mr. Murray, and AAdiich is indeed
almost a necessary sequel to his investigations.
TVe have every reason to helieve, from a series of
ohservations, as yet very incomplete, Avith the toAA'-
net at diiferent depths, that Avhile foraminifera are
F„; TA.— H a liom m a . Sp. ii. Froui th e surface. Tw'o hiuulred times the n a tu ra l size.
apparently confined to a comparatively superficial
belt, radiolariaus exist at all depths in the water of
the ocean. At the surface and a little beneath it the
toAV-net yields certain species; AAdien sunk to greater
depths additional species are constantly found; and in
the deposit at the bottom, species occur AAdiich have
heen detected neither on the surface nor at 1,000
f a t h o m s , t h e g r e a t e s t d e p t h a t AA'hich t h e t o w - n e t h a s
y e t h e e n s y s t em a t i c a l l y u s e d ; a n d s p e c im e n s t a k e n
n e a r t h e b o t t o m o f s p e c i e s w h i c h o c c u r o n o r n e a r t h e
s u r f a c e g i v e u s t h e im p r e s s io n o f h e in g g e n e r a l l y
la r g e r a n d b e t t e r d e v e lo p e d . T h e r e s u l t s f r om t h e
t o w - n e t a r e n o t s o d i r e c t ly s a t i s f a c t o r y a s t h o s e f r om
t h e t r a w l o r d r e d g e , Avhich u s u a l l y b r in g u p a n im a l s
Avhich w e knoAv f r om t h e i r n a t u r e m u s t h a v e liA'ed o n
t h e h o t t o m , a n d i t r e q u ir e s a l i t t l e c o n s id e r a t io n t o
a r r iv e a t t h e i r p r e c i s e v a lu e . We h a v e n o t y e t c o n t
r i v e d a t o w - n e t AA'hich c a n h e s e n t d o w n c lo s e d ,
w h i c h w i l l o p e n i t s m o u t h w h e n i t r e a c h e s a c e r t a in
d e p th a n d c lo s e i t a g a in a f t e r a c e r t a in la p s e o f t im e ;
a l t h o u g h t h e r e i s l i t t l e d o u h t t h a t s u c h a n e t m i g h t
b e m a d e e a s i ly e n o u g h . At p r e s e n t t h e t o w - n e t ,
w h i c h c o n s i s t s s im p ly o f a c o n i c a l b a g o f m u s l in o r
h u n t in e a t t a c h e d t o a n i r o n r in g , i s c o n s t a n t l y o p e n ,
— d e s c e n d in g , d r a g g in g a lo n g , a n d a s c e n d in g . I f
Avorked o n t h e s u r f a c e t h e r e i s o f c o u r s e n e i t h e r d if f ic
u l t y n o r q u e s t io n , h u t i f i t h e b r o u g h t n p f r om
500 f a t h o m s , a t w h i c h d e p th i t h a s h e e n toA v in g fo r
s om e t im e , t h e n e t m a y b e s u p p o s e d t o c o n t a in c h i e f ly
t h e s p e c i e s l i v i n g a t t h a t d e p t h ; b u t m i x e d w i t h t h e s e
t h e r e m u s t h e a c o n s id e r a b l e n u m b e r o f m o r e s u p e r f
i c i a l f o rm s , s om e t a k e n Avhen t l i e n e t Avas g o in g d o w n
w i t h i t s o p e n m o n t h d oA vnw a rd s, a n d m a n y m o r e
c a p tu r e d d u r in g i t s l o n g a s c e n t of h a l f a m i l e t h r o u g h
t h e u p p e r la y e r s . TVe c a n n o t th e r e f o r e a s y e t s a y
Avith c e r t a in t y A vh e th e r t h e s u r f a c e s p e c ie s l i v e
in t h e d e e p e r b e l t s o r n o t , h u t Ave a r e j u s t i f i e d
i n c o n c lu d in g t h a t s p e c i e s Avhich a r e a b s e n t o n
t h e s u r f a c e , a n d p r e s e n t o n l y Avhen a c e r t a in d e p th
h a s b e e n g a in e d , a r e s p e c ia l t o t h a t a n d p r o b a b ly
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