20 BRITISH COPEPODA. 



lescent) external ovisacs attached to the first abdominal 

 segment the coating of the ovisac being formed by the 

 secretion of a special gland, situated near the termina- 

 tion of the efferent duct, an enlargement of which 

 forms in many cases a " receptaculum seminis." In 

 the males the free-living forms have a simple testis ; 

 many of the parasitic and semi-parasitic (Corycceidce, 

 Sapphirinidce) a double testis, with two distinct vasa 

 deferentia, the right duct being sometimes atrophied. 

 In the coiled portion of the duct are formed the 

 spermatophores masses of spermatozoids enclosed 

 in a capsule of hardened mucus, and usually fusi- 

 form or club-shaped. During copulation the male 

 affixes one or more of these bodies near the vulvar 

 aperture of the female, the contents passing into the 

 receptaculum seminis, and fertilizing the ova either in 

 the interior of the body or during their passage into 

 the ovisacs. In some cases the seminal fluid appears 

 to be inserted directly into the vulva without the 

 intervention of a spermatophore. 



THE DEVELOPMENT of the free Copepoda from the 

 moment of rupture of the ovum to the attainment of 

 matured form presents a complex series of metamor- 

 phoses. The parasitic species present some of the 

 best marked examples of " retrograde development" 

 to be found in the whole animal kingdom, but these 

 do not come within the limits of our present subject. 

 The form of the young Copepod on its escape from 

 the egg is that known as NaupUus, having been de- 

 scribed by Muller under that name before its relation 

 to the Copepoda was known. The larva in this 



