168 M.T. Thorell on two European Argulidse. 



along the middle line of the upper surface of the adult animal, 

 and is marked on either side of this median line with large dark 

 spots, arranged in rows. In the sac which is formed by this 

 membrane the eggs are closely packed together, sometimes 

 rather tirmly attached to each other, sometimes apparently quite 

 free. They surround here a smaller, almost cyHndrical organ 

 (the true ovai'ium), to which the innermost eggs are firmly at- 

 tached. I have sometimes found that this organ contained a 

 large number of eggs in a very early stage of development, while 

 those lying outside were fully matured. I conjecture that these, 

 after they are laid and sufficiently matured, becomesevered from the 

 spot where they were formed, and so come to be immediately en- 

 closed in the outer membrane of the ovary. Thus Leydig's sug- 

 gestion that the ovaries in A. foliaceus are " a simple bag " does 

 not apply to A. coregoni. 



The number of the matured eggs is very variable. In a large 

 specimen I have reckoned about 350 points. In appearance 

 they are exactly like the eggs of A. foliaceus. Their length is 

 about I, their breadth about 5 millim. The receptacula seminis 

 are situated, as in ^. foliaceus, at the base of the tail. They 

 have the form of an almost spherical bladder, from which a long 

 channel of communication, with thick walls and a very narrow 

 passage, proceeds to a conical papilla situated in a concavity on 

 the side and somewhat behind the mouth of the ovary. In this 

 passage, rather nearer to the papilla than to the receptacle, is the 

 commencement or opening of another blind, crooked canal, spiral 

 towards the end : in A. foliaceus two such canals are found. 

 The receptacle itself is, in young specimens, perfectly empty, but 

 in the older ones it contains another bladder, of a darker colour. 

 Such is the case also in A. foliaceus, where, according to Ley dig, 

 this inner bladder first shows itself after pairing, and is full of 

 spermatozoids. It seems to be perfectly closed, and may easily 

 be taken out of the receptacle without breaking. Leydig asserts 

 that its membrane is produced in A. foliaceus into a homo- 

 geneous thread, which stretches through the channel as far as 

 the tip of the papilla. I have not found such a thread in A. 

 coregoni. The passage of this channel of communication pre- 

 sents just the same optical appearance in individuals with or 

 without the spermatozoid-bladder already mentioned ; and the 

 passage of the accessory canal is perfectly like that of this chan- 

 nel. If such a thread as that which Leydig speaks of were pre- 

 sent here, it would certainly produce a streak in the canal. 

 Moreover, when the bladder is taken out, a portion of the 

 thread would follow if such were really present ; this, however, 

 does not occur, and I have been equally unable to detect it by 

 cutting asunder the channel of the receptacle. 



