456 Sir H. H. Howorth — The Western Baltic. 



fact in regard to the size of the fish of the Western Baltic compared 

 with those of the North Sea, while their bodies are distorted and the 

 armature of their skins with spines and similar excrescences is more 

 marked. It has also been noticed that the sexual maturity of the 

 animals in these brackish waters arrives earlier than in salt. The 

 stunting of the forms is also true of the worms and Crustaceans, and 

 Braun tells us that the Aurelia, the only worm which reaches the 

 Bothnian Gulf, is only 6 mm. in length there. Norquist has noticed 

 that among the Copepods the same stunting takes place, that it is 

 most marked in the females, and that in the matter of the size of 

 the antennae and furca there is a great variety between the 

 individuals of the same species in the Baltic and the North Sea. 

 Brandt expresses himself most emphatically that this stunting and 

 change, which are thus so general, are due to the gradual sweetening 

 of the water as we advance further from the sea. 



Having examined the distribution and characteristics of the living 

 fauna of the Western Baltic let us proceed a step further. The 

 Cattegat communicates with the Baltic by three passages, the Sound 

 and the two Belts, and in all three thei'e is a marked enrichment of 

 the molluscan fauna as compared with Kiel. This is largely due, no 

 doubt, to the fact that the narrowness of their channels and the 

 speed of their currents cause the indraft of salt water from the North 

 Sea to be less mixed with the fresh-water outward current than it is 

 in the districts further to the south and east, i.e. in the true Baltic. 



The Sound — ' Oresund,' as it is known to the Danes — is much the 

 most important of these water conduits, and the only one of whose 

 zoological features, so far as I know, we have a detailed description. 

 This is contained in the monograph by Orsted entitled "De regionibus 

 Marinis," etc., published at Copenhagen in 1845. He describes it as 

 lying between 55° 20' and 56° 18' N. lat., and as bounded on the 

 north by a line joining Gilleleje and Kullen, while its southei'n limit 

 is a similar line joining Stevns and Falsterbo, Its length is 13 miles. 

 Its greatest width, from Copenhagen to Malmo, is four miles, while at 

 its narrowest, between Kronborg and Helsingborg, it is 6,340 cubits 

 ('cubitorum' is the word used). Orsted divides it into three sections. 

 The most northern, extending as far as Helsingor and Helsingborg 

 respectively, is a mere prolongation of the Cattegat. The middle 

 portion extends as far as Copenhagen and Barseback ; and the 

 southern one, which is a mere prolongation of the Baltic, extends 

 to the southern limit already named. The middle portion is alone 

 properly called the Sound. 



According to Orsted there have been found 427 forms of animals, 

 exclusive of infusoria, in the Sound. These are thus classed : — 



Fishes 



Crustacea 



Arachnida 



Thus, in the class of Mollusca alone the number of species is 

 considerably greater than that of the Baltic, as measured by the 

 havens of Kiel and Flensborg. 



