
836 The American Naturalist. (September, 
plexus for the pineal organ in these forms. In Ichthyophis, on account 
of the enormous folding of the arterial plexus the roof of the thalam- 
encephalon is completely covered. It falls into an anterior wall, 
` embraces the ganglia habenulz on either side, and a posterior wall 
between the posterior and superior commissures, At the spot where 
these swellings meet is a small pear-shaped vesicle, which extends into 
the space between the hinder part of the arterial plexus and the roof of 
the thalamus. Development shows that this is the pineal organ. In 
Protopterus the pineal organ is a small, irregular sac, which extends 
directly upwards from the boundary between the mid- and twixt-brains 
into the abundant connective tissue of that organ. Burckhardt has 
not yet traced its lumen into connection with.the third ventricle. 
Foetal Period of the Seal.—Grieg has studied the period of 
pregnancy of Phocena communis.“ He analyses the known literature, 
and finds great diversity of opinion. He then studies thirty-five 
embryos, with dates of capture of the mother, and comes to the con- 
clusion that the period is about nine or ten months. According to the 
Norwegian fishermen, copulation takes place usually in July and Aug- 
ust; but he finds that the breeding season may extend, according to 
locality, from July to October, and the young are born from March to 
June. At the time of birth the young measure from 700 to 860 milli- 
meters, and may reach a length of 880 millimeters. 
Extent of the South American Fresh-Water Fish 
Fauna.—There are more fresh-water fishes in the neotropical than in 
any other region. A comparison made by Carl and Rosa Eigenmann 
of the latest lists of European and North American fresh-water fishes, 
with alist of the South American species, shows the extent of the South 
American fauna. In summing up the species they find 126 European, 
587 North American, and 1,147 South American species. (Proceeds. 
U. S. Nat. Mus., Vol. XIV., pp. 1-81.) 
The Chromididz of the Fresh Waters of Madagascar.— 
One of the most interesting peculiarities of the fresh-water fish fauna 
of Madagascar is the presence of the Chromididz, coincident with the 
absence of the Cyprinide and the Characinide, although these two 
groups are found in Africa, and the great paucity of Siluride, so that 
the Chromidide are, so to speak, the only fresh-water fishes of this 
large island. i 
At the present time the Chromididæ are a family of South America 
and of Mexico, 230 species out of 260 having been described from 
that region. 
10 Jena Zeitschr., XXV., 544, 1891. 





