PISCES 467 



that the budding portion corresponded with the centre of the 

 daughter's body, and this, in a little while, assumed the aspect 

 o a semicircular band. Subsequently the upper end became 

 detached, the freed extremity being now recognised as the 

 head. An interval elapsed before the broad posterior end of 

 the animal could be disengaged, but immediately after this was 

 effected the sides of the parent envelope closed in upon the 

 opening, and all that remained was a small cavity or sac, 

 indicating the position recently occupied by the daughter. 

 Altogether the process occupied about five minutes. I care- 

 fully compared the so-called " parent " with the " daughter/' 

 but in regard to sige I can scarcely say which was the larger of 

 the two. As before hinted, Van Beneden demurs altogether to 

 Yon Siebold's views. He does not admit the parent to be a 

 kind of " nurse," he does not consider the primary young one 

 to be a "daughter," and, consequently, he does not regard the 

 embryo seen within the latter as a "grand-daughter." Yan 

 Beneden says : " According to our researches there is here a 

 false interpretation ; the little daughter is lodged within the side 

 of its pretended mother, and not in its interior ; instead of 

 being its mother, it is its sister; there is a difference of shape 

 because there is a difference of age ; the Gyrodactyles are vivi- 

 parous, and as among the Trematodes the eggs are formed one 

 by one, one embryo is scarcely formed when another commences 

 its evolution, and the egg- deposition is effected even whilst the 

 embryo is being produced, i The Gyrodactyles are therefore 

 viviparous worms, which beget a single embryo at a time, as 

 those of the trematode group, to which they are allied, beget a 

 single egg at a time, and before the first embryo is expelled 

 another is already partly developed. There, we believe, lies the 

 correct interpretation of that phenomenon ; instead of a bud it 

 is an embryo, which has escaped from an egg.. Here, therefore, 

 we have no phemonenon of alternate generation or of digenesis, 

 as Yon Siebold supposes, but a simple viviparous reproduction." 

 Passing on to notice the cestodes of fishes, I may remark i 

 that they often display characters very distinctive from those 

 inhabiting birds and mammals, being commonly furnished with 

 special tentacular hook-appendages employed as supplementary 

 organs of boring and anchorage. In the cartilaginous sharks 

 and rays these cestodes are remarkably abundant, and in certain 

 osseous species they are scarcely less frequent. The only 

 noteworthy kinds of fish which are commonly free from the 



