ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
429 
Malay Archipelago. After some account of the observations and con- 
clusions of previous writers, he states that he proposes to follow the 
classification of Langerhans, although he recognizes that it is defective in 
some particulars. He gives a diagnosis of the genus Sagitta , of which 
he found a new species which he calls S. bedoti. In addition to this, 
three already described species were recognised by him in the collection. 
Of Spadella he forms a new species, which he calls S. voujai. The 
author is of opinion that we shall have to carefully distinguish between 
such pelagic species as are cosmopolitan, and such as are restrained to a 
definite area. With regard to their habits, there appears sufficient evi- 
dence that these voracious worms do not hesitate to eat their own kind. 
Platyhelminthes. 
Distribution of Planarians.* — Dr. W. Yoigt discusses a case in 
which Planaria gonocephala seems to be in the act of extending its 
range up-stream into the region of Planaria alpina and Polycelis cornuta. 
He considers the possible ways in which the range of a Planarian may 
be extended. It or its cocoon may be carried by bird or amphibian ; 
but the transport of the whole animal is probably infrequent in the case 
of those inhabiting mouutain streams. Moreover, a few minutes’ expo- 
sure weakens them greatly, and an hour’s exposure may be fatal. There- 
fore the passive distribution of Planarians is probably for the most part 
in the cocoon-stage, which resists desiccation with some success. But 
the likelihood of cocoon transport varies in different species ; thus PL 
gonocephala lays its cocoon under a stone, Pl. alpina free on the bottom. 
The extension of range on the part of PL gonocephala which the author 
believes to be occurring is too regular to be due to passive transport ; 
the animal is actively spreading. The author gives facts showing that 
the present retreat of PI. alpina before Pl. gonocephala cannot be 
explained by conditions of temperature, chemical composition of the 
water, nutrition, or the like. He observes that Pl. alpina appears to be 
shy of the larger Pl. gonocephala, though it is never attacked by its 
fellow species. Probably the slime is disagreeable. But as this holds 
only for immediate proximity, it cannot be a reason for the retreat of 
PL alpina before Pl. gonocephala. Nor, as the author shows in detail, 
is this to be explained in reference to the enemies or the food-supply of 
the two species. It must be granted, however, that Pl. gonocephala is 
the stronger, much abler, for instance, to capture a Gammarus ; its habit 
of laying its cocoon below a stone is also advantageous. As Kennel has 
suggested, the facts of distribution lead to the conclusion that Pl. alpina 
and Pol. cornuta are relicts of the Glacial epoch. Yoigt supposes that 
they had in pre-Glacial times reached the higher regions of the streams ; 
while Pl. gonocephala frequented those lying lower. As the Ice Age set 
in the two former species retreated, with other freshwater animals, from 
the mountains to the plains. Now if Pl. gonocephala, with Dreissenssia 
polymorpha and others, perished in Middle Europe, but subsequently 
returned from warmer regions to the old home, the distributional facts 
which Yoigt has observed would be explained. It should be further 
noted that PL alpina lays its cocoons from December to May, and that 
* Zool. Jahrb. (Spengel) Abth. Syst. Geogr. Biol., viii. (1894) pp. 131-76 (3 maps). 
1895 2 F 
