ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA 67 



■' quite new form " of propagative organ. From the mode of expres- 

 sion in the foUowing paragraph he evidently thinks the propagation 

 here to be in some manner sexual. " Die Eintheilung in Strecken 

 deren jede Fotus von einerlei Ausbildung enthalt, deutet allzu 

 bestimmt auf verschiedene Befruchtungen hin, als das hier nicht eine 

 wiederholte Geburt in langeren Zwischenzeiten anzunehmen ware." 



Sars conjectures that the solitary foetuses arise by a process of 

 sexual generation, but does not state very clearly what he considers 

 to be the nature of the production of the associated forms. 



"]"]. The Placenta. — Cuvier speaks of finding a foetus attached to 

 the parent by a pedicle ; and referring to a figure, he says : " Ce corps 

 rond (evidently the placenta) seroit-il un organe servant uniquement 

 pendant le temps de la gestation pour etablir I'union entre la mere et 

 son petit et qui s'effaceroit ensuite ? " 



Chamisso calls the pedicle of attachment " pediculus umbilicalis ; " 

 the placenta " globulus opacus.'' 



Meyen was the first to give this structure the name of placenta, and 

 his account of it is so very clear and precise, that it is wonderful it 

 should have been subsequently forgotten or overlooked. He says, 

 "Wir haben bei ganz jungen Individuen den Verlauf der Blut- 

 bewegung selbst bei 200-maliger Vergrosserung beobachten konnen. 

 Der Muttertheil der Placenta hat nur wenige Gefiissen um so mehr 

 aber der Fotus-theil, in dem sich ein ausserordentliches Convolut von 

 Gefassen befindet, das sich in einem Stamme endigt, der sich in das 

 grosse Bauchgefass ganz in der Nahe des Hergens ergiesst. Ein un- 

 mittelbares uebergehen der Blutgefasse ausdem Mutter-theil in dem 

 Fotus-theil haben wir nicht sehen konnen. Hat der Fotus die 

 hinlangliche Ausbildung im Leibe der Mutter erreicht, so verwachst 

 das grosse Blut-gefass und die Placenta fallt ab." — P. 400. 



78. After what has been stated concerning the development of the 

 two forms of the Salpce, it would be useless to enter upon the con- 

 sideration of the various theories propounded since the time of 

 Chamisso (such as that of Eschricht for instance) to account for 

 the phenomena they present. 



It may be sufficient to say, that it is now quite certain that the 

 SalpcB never unite after being once separated, and that they do not 

 produce successive broods of a different form. 



Much remains to be done with regard to the minute process of 

 development of the young forms of both kinds, and to this difficult 

 inquiry it is to be hoped that future observers will address themselves.^ 



1 An essential service to zoology will be rendered by any one who will revise and critically 

 compare the species of the Saljxs. At present, they are in a most unedifying state of hopeless 

 confusion. 



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