70 LIFE IN THE SEA [PART I 



The larvae which hatch out from these eggs are the Zoeas and 

 these judged by microscopic standards are fairly big creatures. 

 Zoeas have a comparatively long life in the sea as pelagic animals 

 before they undergo their first metamorphosis into the Megalopa 

 stage, and the megalopa has also a somewhat long life in this 

 stage. By-and-by the megalopa, by repeated moults, passes into 

 the adult stage and the Decapods then settle down to the sea 

 bottom for the remainder of their natural lives. At times the 

 tow-nets may contain nothing else than the zoea or megalopa 

 stages of crabs. Just so the shrimps and prawns appear also in the 

 plankton in their larval stages. Other groups of Crustacea, the 

 Isopods, Amphipods, Phyllopods and Stomatopods, terms which 

 the unprofessional reader will understand as connoting groups of 

 Crustacea distinguished by well-marked variations in structure, 

 also occur in the plankton, at times in quantity. Some are 

 permanent planktonic animals, while others live on the sea bottom 

 as adults and only appear among the pelagic life of the sea in their 

 larval stages ; but many others, many of the Schizopods and 

 Ostracods, are permanent inhabitants of the free ocean and shallow 

 seas. 



The crustacean animals known as the Copepods are by far the 

 most abundant metazoan animals living in the sea. Some of the 

 single celled animals or protozoa may surpass them in number, but 

 the importance of the copepoda in the economy of the sea depends 

 not only on their number but also on their size, and many 

 thousands of some of the smaller protozoa may not have the bulk 

 of a single large copepod. The copepoda are small creatures, the 

 average length of which in our seas may be put at about one- 

 sixteenth of an inch. They are quite ubiquitous. It is so rarely 

 that a tow-netting can be taken without including some of these 

 micro-crustacea that when this occurs the planktologist feels 

 that the occurrence is worthy of special remark. The copepods 

 are for the most part pelagic in habit, but a very considerable 

 group of them is found in the mud and sand at the sea bottom, 

 and some have adopted a parasitic habit and live on the outsides 

 of many fishes. The pelagic forms have as the figure shews, a some- 

 what cylindrical body, ten pairs of appendages, two pairs being 

 feelers, and a jointed tail furnished with hairs (the importance of 



