SEA-FISHERIES LABORATORY. 199 



founded the last fin ray was characterized by its sigmoid 

 curve and horizontal position. These features T»ere doubt- 

 less anomalies. 



10.— Anal Fin (Figs. 18 and 19). 



The mechanism of the fin rays and their skeletal 

 supports is the same as in the dorsal fin. The axonosts 

 are, however, perceptibly longer than those of the latter 

 fin, and they are sometimes called interhaemal bones to 

 distinguish them from the interspinous elements. The 

 structure of the anal axonosts is the same as that of the 

 dorsal ones. 



The anterior extremity of the anal fin is interesting 

 in many ways. The posterior boundary of the body cavity 

 is supported by a very stout bone which curves downwards 

 and forwards from its roof, and terminates in a point 

 behind the anus. Above it fits into a deep recess borne 

 on the anterior face of the haemal spine of the first caudal 

 vertebra (fig. 13, Rec.Ax. 1 ). The ventral point, to an 

 extent indicated in fig. 18 by a ring, is in dead specimens 

 almost invariably found perforating and projecting freely 

 through the skin behind the anus. It seems highly im- 

 probable that such a pathological condition can obtain 

 during life, but the skin covering the point must be very 

 thin.* This bone, in the lack of any evidence as to its 

 development, is here called the first axonost, but it is 

 certain that it is more than this. In no other part of the 

 body is a baseost situated anywhere but between two 



* We are now certain that the point does not perforate the skin during 

 life, but that the latter is somewhat easily ruptured when a plaice is 

 handled K and allows the point to protrude. Also that the protrusion in dead 

 specimens is due to contraction following on preservation. To make use, 

 therefore, of this so-called external " anal spine " in classification, as has 

 hitherto been done, is absurd. Since this was written, we note that Kyle 

 arrives at the same conclusion. 



