EFFECT ON ASCIDIANS AND MOLLUSKS. 43 



those adherent to the skins of various whales), send off a 

 multitude of free-swimming young which often crowd the 

 inshore water, and extend far beyond before settling down 

 on every available surface. Many other instances of the pleni- 

 tude of crustacean pelagic life, and its adaptation for the 

 nourishment of fishes, might be given, but sufficient has been 

 cited to show that, besides the crustaceans of the bottom, those 

 frequenting the water itself must be considered. 



The ascidians or ' sea-squirts ' of the bottom are occasionally 

 brought up in the trawl attached to shells, stones, and sea- 

 weeds ; and such forms, along with pieces of ' sea-mat,' are not 

 unfrequent in the stomachs of cod and haddock. They are 

 usually sent overboard in a condition by no means unfavourable 

 for existence, though it has to be stated that numerous pieces 

 of adherent sea-mat are often brought to shore on the ground- 

 rope and meshes of the trawl from certain areas. The young 

 ascidians are free-swimming (tadpole-like), and escape inter- 

 ference till they settle on shells, stones, and sea-weeds. An 

 interesting species in this group (Oikopleura or Appendicularia) 

 is pelagic throughout life, and often occurs with its gelatinous 

 ' houses ' in dense multitudes in our inshore waters. It lives 

 upon microscopic plants and similar structures in the water, 

 while the smaller fishes and other forms prey on it. 



The last group of the invertebrates liable to injury by the 

 trawl is that of the shell-fishes and cuttle-fishes (Mollusca). 

 In 1884 the opinion expressed was that, 'amongst the mollusks, 

 the nudibranchs suffer a little on^ deck, but the cuttle-fishes 

 are more delicate, the majority being almost lifeless on removal 

 from the net. The horse-mussels are occasionally fractured, 

 but the whelks are uninjured.' With the exception of water- 

 logged wood bored by the ship-worm, horse-mussels, and whelks 

 of various kinds, the majority of the shells brought on board 

 were old and empty, either covered with growths of various 

 kinds, such as zoophytes, or harbouring star-fishes and annelids 

 in their interstices. As a rule, the horse-mussels were un- 

 injured, and were consigned in safety to the water with the 

 debris. On some of these such delicate organisms as the 

 spawn of the Norwegian whelk (Fiisus norvegicus), with the 



