THE COPEPODA 



97 



originates to the outer (or dorsal) side of the exopodite, and is bent 

 backwards upon the protopodite. It is provided with two rows of 

 plumose setae, and its probable function is to cleanse the lower 

 surface of the carapace. The homology of this appendage is 

 doubtful. It cannot be an epipodite since it springs from the 

 distal segment of the protopodite. Nothing equivalent to it is 

 found in the Eucopepoda. 



In the male sex the peduncles of the last two, sometimes of the 

 last three, pairs of legs are modified for purposes of copulation. 

 The details differ in the different species, but in all the peduncle of 

 the penultimate pair is excavated to form a seminal pouch which 



ovy. 



-f-b. 



Fio. 55. 



A. ii'Tvou-i systria of Argvlusarnericanitfs. e, nauplius-eye ; immediately below is theopening 

 through which the oesophagus passes. B, female reproductive organs, ovy, ovary; od, open- 

 ing of oviduct : .-71, spi-rmatheca : the papillae on which the spermathecal ducts open are seen 

 just below the opening of oviduct ; t.p, "tactile papillae." C, male reproductive organs, gl, 

 accessory gland ; o, external opening ; .v, seminal vesicle ; t, testis. (After Wilson.) 



opens on the dorsal surface of the limb. On the anterior surface 

 of the peduncle of the last pair is a peg-like process which seems to 

 be used for opening the mouth of the seminal pouch so that the 

 latter can be filled with sperm. In some species in the female sex 

 u pair of finger-like processes (Fig. 55, B, t.p) are situated at the 

 sides of the genital orifice between the last pair of legs. These 

 may possibly represent a vestigial sixth pair of thoracic appendages. 

 In the genus Argulus a very peculiar poison apparatus is 

 situated in front of the mouth. It consists of a hollow spine (Fig. 

 r>4, .s/>), which can be withdrawn into and protruded from a sheath 

 by the action of special muscles. The duct which traverses it com- 

 municates with three groups of large unicellular glands lying at its 



