65 
These parasites vary considerably in size, ranging from 
one-thirtieth of an inch to nearly two inches in length. 
They also differ very much 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 off 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 the females, especially those of the 
Chondracanthide and Lerneopodide. 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 hfe. The resulting 
embryos remain attached to the external opening of the 
oviduets, 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 
b 
