3 



These parasites vary considerably in size, raiig-iug- from 

 one-thirtieth of an inch to nearh' two inches in leng-th. 

 They also differ very much in shape. Some have theii' 

 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 offc' their host 

 they 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 ihe females, especially those of the 

 C'hondracanthidae and Lernseopodidae. 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. I'ertilisation of the female is 

 effected early in its life history, before the metamorphosis 

 i'^ completed. One copulation, apparentlj', 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, hnally 

 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 



