190 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



These parasites vary considerably in size, ranging from 

 one-thirtieth of an inch to nearly two inches in length. 

 They also differ very mnch in shape. Some have their 

 locomotor organs well developed, and are capable when 

 necessary of leading a pelagic life for a period. Others 

 have lost all swimming power, and become mere inert 

 sacs, securely attached to their host by anchor processes, 

 embedded in the tissues, and when taken oif their host 

 the} r soon die from want of food and oxygen. 



The sexes are separate, the males as a rule being much 

 smaller than the females. In many cases the males are 

 practically parasitic on the females, especially those of the 

 Chondracanthidse and Lernaeopodidse. The fact that the 

 males are found upon egg-bearing females of the above 

 families is due to their power of locomotion having been 

 lost when they reached maturity. When once they have 

 settled down and matured they are unable to change their 

 position to any extent. Fertilisation of the female is 

 effected early in its life history, before the metamorphosis 

 is completed. One copulation, apparently, is all that is 

 necessary to fertilise the female for life. The resulting 

 embryos remain attached to the external opening of the 

 oviducts, either in a single or multiserial column, enclosed 

 in a sac, until they hatch. The period of incubation 

 extends over several weeks. The young parasites hatch 

 out as nauplii, with three pairs of appendages. The 

 nauplii undergo metamorphosis, which in some forms 

 after a certain stage is reached is retrogressive, finally 

 leading to the adult condition. 



The Copepod fish parasites are generally regarded as 

 being composed of about sixteen somites. Usually, how- 

 ever, some of these somites are suppressed or fused 

 together, forming one compound segment, the true 

 character of which is rendered evident by the appendages 



