On an undescribed Organ in Limulus. 250 
first two have intimate relations to each other, and (4) the last 
three others among themselves; and some weighty arguments 
may be adduced to support a division of the faunas of the 
globe into two primary regions coinciding with the two com- 
binations alluded to—(a) a CmNnoG#Aa and (6) an Eocama, 
which might represent areas of derivation or gain from more 
or less distant geological epochs. 
In connexion with the geographical distribution of fishes 
there are a couple of empirical facts which are also specially 
noteworthy. In the order of Teleocephali the Acanthoptery- 
gian types are vastly preponderant in the tropical and sub- 
tropical waters, while the jugular Malacopterygian types 
(e. g. Lycodide, Gadide, &c.) form a large proportion thereof 
in the polar regions. F urther, and it is in the same direction, 
in Acanthopterygian types the vertebre are actually or ap- 
proximately 24, divided between 10 abdominal and 14 caudal, 
im the great majority of the tropical saltwater species ; while 
in the cold-water forms (arctic and antarctic) the number is 
considerably increased. There are many exceptions to this 
generalization so far as the tropical forms are concerned ; 
but the tendency in the direction im question is so decided, 
that while in the warm-water forms of the typical Scor- 
penine (Sebastosomus, Scorpena, &c.) the vertebre are 24 
(A. 10 +C. 14), in the representatives which are peculiar to 
the high north (Sebastes norvegicus and S. viviparus) the ver- 
tebre are increased in number to 31 (A.12+€C.19). There 
is, however, no apparent physiological or morphological corre- 
lation between these and other facts, and we have m them 
perhaps nothing more than interesting cases of irrelative 
coincidence. 
XXXUI—On an undescribed Organ in Limulus, supposed 
to be Renal in its Nature. By A. S. Packarp, Jun.* 
In dissecting the king crab one’s attention is directed to a 
large and apparently important gland, conspicuous from its 
bright red colour contrasting with the dark masses of the 
liver and the yellowish ovary or greenish testes, and present- 
ing the same appearance in either sex. The glands are 
bilaterally symmetrical, one situated on each side of the 
stomach and beginning of the intestine, and each entirely 
* From an advance sheet of the ‘American Naturalist,’ communicated 
by the Author, having been read at the Philadelphia Meeting of the 
National Academy of Sciences, held in November 1874. 
182 
