CHINESE MITTEN CRAB — PANNING 



365 



maturity, they naturally moved on downstream into the Baltic in 

 their hunt for salt water. And they may have come through the 

 North Sea — Baltic Canal (Kiel Canal) as well. They have spread 

 from these breeding grounds in the Great and Lesser Belt in the 

 Baltic to Denmark, southeastern Sweden, East Prussia, southern 

 Finland, and in some instances, to some of the adjoining countries on 

 the Baltic. Today, according to Dr. Peters, lower and mid Elve as 

 far as into Saxony, the Weser below Bremen, and the coast regions 

 of Germany and Holland from the Elbe to the Rhine are thickly 

 infested with them. In other sections they are only sparse (fig. 2). 



DEUTSCHLAND 



Figure 2.— Distribution of the Chinese mitten crab; horizontal lines: now inhabited region; dotted region: 



very heavily inhabited. 



REPRODUCTION 



The mitten crab is, during its whole life, practically a fresh-water 

 animal and is found hundreds of kilometers upstream in thickly in- 

 fested rivers. With the development of the sex instinct, the urge for 

 the sea also awakens in them, and in August, or after, they leave their 

 feeding grounds, often located far inland, to move on downstream to 

 the sea. The sex organs develop during this migration and the crabs 

 reach puberty on the last lap of the journey through the usually brack- 

 ish water in the tidal regions. In the fall they always gather to breed 

 in large swarms in the brackish water in the lower course of the rivers. 



