1890.] REPETITION OF PARTS IN ANIMALS. 58/ 



of a Herring. From these points of structure Mr. Day concluded 

 that the specimen was a hybrid between the Herring and the 

 Pilchard. 



Before discussing the propriety of this view, I will describe two 

 specimens showing somewhat similar characters, which were given 

 to me by Mr. Dunn during the summer of 1889. Mr. Dunn told 

 me that among the large number of Pilchards which come under 

 his notice as director of the pilchard-curing factories at Mevagissey, 

 specimens showing this singular reduplication of the scales on one 

 side are not uncommon. Owing, however, to the fact that the fresh 

 Pilchards are shovelled wholesale into the brine-vats, it is generally 

 not until the fish are picked over for packing after the salting 

 process that any individual peculiarities are noticed. This was the 

 case with the present speciniens, which were given to me as they 

 came salted from the presses. Nevertheless, when received, they 

 were in good condition. 



The first specimen measures 8 inches to the base of the caudal 

 fin. The head and opercula of both si4^s are normal. The number 

 of scales along the lateral line on the left side is 32, and the number 

 on the right side is 56 or 57. Examined closely, it can be seen that 

 for the distance of about an inch behind the operculum the scales 

 are not much smaller than those of the normal Pilchard, but that 

 behind this point each scale is of about half the normal size. 



The second specimen difi'ers from the first in that the reduplication 

 occurs on the left side instead of on the right. Furthermore, the 

 scales are normal in size as far as the anterior end of the dorsal fin, 

 behind which place they are of about half the normal size. The 

 transition is much more abrupt in this specimen than in the other. 

 The scales of this fish had been somewhat rubbed, and I was not 

 able to satisfy myself of the accuracy of the counting, but the total 

 number along the lateral line was approximately 48. 



In the figure of Mr. Day's specimen, given in P. Z. S. 1887, pi. xv., 

 no transition is indicated between normal and abnormal scales, but 

 there is a general appearance of uniformity. 



These three specimens aU agree in showing repetition of the scales 

 on one side. The distance to which this repetition extends differs 

 in each case, but in aU the condition of the scales is uniform and 

 regular so far as it extends. In my judgment these specimens 

 should be considered as examples of variation in number of parts. 

 Since, however, it has been suggested that they are of hybrid origin, 

 a few words may be permitted in criticism of this view. 



No direct evidence is adduced which points to hybrid parentage. 

 The suggestion is derived from (1) the condition of the scales, (2) 

 the number of the gill-rakers, (3) the alleged difference in the 

 opercula of the two sides. In view of the first point, viz. that the 

 number of the scales on one side is intermediate between that of the 

 Pilchard and that of the Herring, it seemed desirable to know 

 whether the resemblance extended to the minute structure of the 

 scales or was restricted to their number only. On comparing 

 microscopically the scales of the Pilchard and the Herring, I find 



