108 Racial Studies in Fishes 



White Sea in the north to the English Channel in the south, is common 

 on the east coasts of Scotland and England but rare on the west, and is 

 not known with certainty from Ireland. Eastward, however, it pene- 

 trates into the innermost waters of the Baltic, to the base of the Gulf 

 of Bothnia and Gulf of Finland. A striking feature is the fact that it 

 is not found at the Faroes or Iceland. 



One of the most prominent points in the natural history of Zoarces is 

 that it is viviparous. Pairing takes place late in the summer, and by 

 the close of the winter a considerable number of young, up to 400, are 

 brought into the world. These are at birth 4 — 5 cm. long, exactly 

 resembling their parents in all main features, and, like these, keeping 

 to the bottom from the very first. The quality of being viviparous is 

 almost unique among our northern teleosteans, and this is also one of 

 the essential reasons for my taking Zoarces for the purposes of investi- 

 gation, as we have here the great advantage of being able to examine 

 the progeny of a single female and compare the qualities with those of 

 the mother. For the young have, before they are born, all the qualities 

 with which we are here concerned fully developed in numerical respects. 



Besides a great number of characters which have not been investi- 

 gated throughout in all samples, we have devoted particular attention 

 to the following four: (1) number of vertebrae ("vert"), (2) of rays in 

 the right pectoral fin (" Pd "), (3) of hard rays in the dorsal fin (" D^ "), 

 and (4) of pigment spots on the dorsal fin (" Pigm. D^ "). All these 

 qualities are determined by counting, so that we have only to deal with 

 integrated variates. This is an advantage, as the qualities in question 

 are not altered from long before the birth of the individual until its 

 death. 



The characters investigated are of essential physiognomical impor- 

 tance, the number of pectoral rays, however, to a lesser degree than the 

 others. This will be seen from the three sketches (PI. VII, figs. 1 — 3). 

 The specimen shown in Fig. 1 has a large number of vertebrae, viz. 121, 

 and thus appears much more slender than those in Figs. 2 and 3, with 

 105 and 109 vertebrae respectively. 



Highly characteristic of Zoarces is the fact that the dorsal fin has an 

 incurvation extending for a more or less considerable length down its 

 posterior part. This portion of the fin contains only hard rays, the 

 number of which will thus determine the length of the incurvation. 

 In the specimen Fig. 1, where there are no less than 12 hard rays, the 

 incurvate part is long ; in the specimen Fig. 2, where the number is 

 only 5, it is much shorter. Finally, the dorsal fin in the specimen 



