158 



Proceedings of the Boyal Physical Socieiy. 

 niarium. As it was advisable to keep 1 



to the Aquarium. As it was advisable to keep the speci- 

 mens under constant observation, the large tanks of the 

 establishment were considered unsuitable, and the majority 

 of the fry were placed in a series of wood hatching-trouglis 

 similar to those used for trout ova. A few were also placed 

 in a glass jar, in order that their habits might be watched. 

 Having given instructions for the proper feeding of the fry, 

 I left Eothesay for two or three days. On my return I was 

 much disappointed to find that the whole of the specimens 

 placed in the w^ood troughs liad died, whilst there had 

 scarcely been a death amongst those placed in the glass jar. 

 This was a severe lesson, and showed clearly the unsuit- 

 ability of wood hatching-boxes for marine forms. For fresh- 

 water fishes they serve very well, but unless coated with 

 asphalte or some similar substance, I have frequently found 

 them to prove fatal to delicate marine embryos. Those in 

 the glass jar lived well for some time, but there were occa- 

 sional deaths. The young fry fed freely on copepods, and 

 the smaller forms of amphipods. At first they swam near 

 the surface, and always looked upwards for food. They 

 could not be induced to take food at the bottom for several 

 weeks. Later, as the fan-like ventrals became more and 

 more reduced, they began to rest more at the bottom, until a 

 time arrived when they ceased to feed in the former manner, 

 and now always searched the bottom of the jar for food. 

 There appears little doubt that this change in habit is a natural 

 one, associated with a change in food, in which case the 

 large larval ventrals must be of especial use, and enable the 

 embryo more readily to maintain itself near the surface of 

 the sea during the period when its natural food is to be 

 found there. A similar pelagic habit is, however, common 

 to the larvse of most marine fishes irrespective of the con- 

 dition of the ventral fins, and all feed at first on small 

 pelagic organisms. The specimens were so far advanced by 

 Christmas, that the species could be recognised, and by the 

 end of February one specimen had assumed all the characters 

 of the adult, and measured nearly 2h inches in length. 



The species to which they belonged — Motella cimhria — is 

 usually regarded as one of the rarest of the r>ritish Motella\ 



