19 



side, which ramify throughout the larger portion of the carapace. 

 It has been suggested that these ventral branches serve as a store 

 for food, so that the Argu/iis is enabled to live for several days, or 

 even weeks, away from its host. 



The reproductory system will now be considered. The generative 

 organs having been described, I will give a short summary of my 

 observations on the copulation of the Argulus. This frequently 

 takes place when attached to the fish, and at this period the female 

 is seen to be full of ova. The male takes up a position on the back 

 of the female and places the tail-plate underneath that of the 

 female. The third and fourth feet of the male are seen to be clasped 

 together at their bases, the branches of which are bent under. 

 This position is taken up alternately with either lobe of the female 

 tail-plate, and contact appears to take place just over the recep- 

 taculum. The corresponding feet on the opposite side of the male 

 are held motionless during this time, whilst the first two pairs of feet 

 continue their usual movements. Under the microscope the semen- 

 capsule on the third foot of the male is seen from the dorsal side to 

 be placed under the tubercle on the fourth leg. It appears to me 

 that the semen is transferred to the receptaculum from the male 

 semen-capsule by means of this tubercle, possibly by pressure 

 thereon, but exact observation is very difficult, if not impossible. 

 The change in the appearance of the semen-capsule from opacity to 

 transparence, before and after copulation, has already been noticed. 

 Copulation may be performed with either side of the organs of both 

 male and female. Claus says that the female requires copulation 

 on both receptaculi. Leydig is of opinion that the capsule of the 

 male is placed over the papilla of the female. Copulation may last 

 during several hours. 



Oviposition. 



Under natural conditions ovipositing commences about the end 

 of April. There are at least two broods during the year. In con- 

 finement I have records of ova laid on November 29th and hatching 

 on May 6th the following year ; also others laid as late as December 

 27th, when the weather was very cold and frosty. On the other hand, 

 some batches laid on August 30th and September 2nd remained over 

 the winter and hatched on April loth. I have also observed 

 two batches of eggs hatched on February 27th, when the weather 

 was mild, and continue hatching throughout March. These became 

 adult on June 27//^, and laid ova which hatched 0)1 July 20th (23 days). 



Statistics which I have taken from twenty cases of oviposition show 

 that the average time for the laying of the egg until hatching occupies 

 twe7ity-five days, and hatching continues over three or four days. 

 The opinions of competent authorities differ widely on this point. 

 Temperature no doubt influences the length of period between ovi- 

 position and hatching, for I find that the later broods before hatching 



