218 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



incubation was found to extend over several weeks at 

 least. In one case the ovisacs were kept for six weeks, 

 and in another eight weeks, before the embryos hatched. 

 The incubation takes longer than that, however. In 

 both cases the embryos were pigmented when placed 

 under observation. The first appendages that make their 

 appearance are the antennules, antennae and mandibles. 

 They are in a rudimentary state, and the embryo is now 

 ready to hatch. During this period the embryo increases 

 in size as it develops. 



The whole of the embiyos contained in the tube hatch 

 practically at once. The enclosing membrane ruptures, 

 then the membrane of the tube splits, and the nauplii 

 after freeing themselves from the fragments swim to the 

 surface. Plate L, fig. 3, represents a newly hatched 

 nauplius, the natural size of which is '46 mm. It leads 

 a pelagic life for a time, and grows by successive moult- 

 ings. It next settles down on some fish, and passes into 

 a cyclopoid state (Plate I., fig. 5). The young parasite 

 immediately develops a thin chitinous filament from the 

 median frontal gland already described, which passes into 

 the tissues of the host, and it becomes fixed. The median 

 sucker (b., Plate I., fig. 5), with the help of the rudi- 

 mentary antenna? and second maxillipedes, enables the 

 animal to bring its mouth into contact with the host. 



If young plaice, flounder, cod, &c, one to three inches 

 in length, be examined very carefully at the end of the 

 summer, it is practically certain that some recently 

 attached Lepeophtheirus or Caligus will be found either 

 on the fins or some other part of the integument. On 

 examining fins which have parasites attached, the filament 

 is seen passing through the skin, under it, and along one 

 of the fin rays, as shown on Plate I., fig. 5 (natural size 

 '77 mm.). The filament may have the end bluntly 



