FISHES 215 



a shell, the female lays her eggs on the lower surface of the 

 shell, and the male then guards them and keeps up a circula- 

 tion of water by the motion of his pectoral fins. Sexual 

 differences, both of structure and colour, exist in these species, 

 but to a much less degree than in Callionymus. In the male 

 Gdbius minutus the colours of the male are brighter and more 

 intense than those of the female, at least in the breeding 

 season. The breeding habits of these species have been 

 minutely studied by a French naturalist, Guitel. 1 The males 

 of G. minutus were found to fight for the possession of the 

 females, and the fights were serious, the females being left to 

 the victors. 



Aphia pellucida and Crystallogdbius Nilssonii are two 

 small species of the Goby family, which are believed to spawn 

 only once and then die. In both, sexual differences of 

 structure are rather strongly developed. In Aphia, in both 

 females and immature males, the teeth are small, of uniform 

 size, in a single row. In mature males these teeth are re- 

 placed by another row of longer pointed ones, and the dorsal 

 and ventral fins become higher, especially in the hinder part. 

 The whole head becomes thicker and the body plumper. The 

 fish does not exceed 1J inch in length. It is taken in 

 depths of 1 to 15 fathoms, on the British and Norwegian 

 coasts. 



In Crystallogdbius the females are slender with pointed 

 heads and toothless jaws. Their first dorsal and pelvic fins 

 are rudimentary. In the young males the head is somewhat 

 pointed, but contains teeth. In the mature male the snout 

 becomes short, the extremity of the mandibles is curved up- 

 wards and received into a notch in the upper jaw. At each 

 angle of the projection of the mandible is a long tooth. The 

 first dorsal consists of two rays, and the second dorsal and 

 ventral (anal) are broader than in the female. The fish, like 



1 Arch, de Zool. Experimcntale, 1892 and 1895. 



