592 
MR. HUXLEY ON THE ANATOMY OF SALPA AND PYROSOMA. 
graph he evidently thinks the propagation here to be in some manner sexual. “ Die 
Eintheilung' in Strecken deren jede Fdtus von einerlei Ausbildung enthalt, deutet 
allzu bestimmt auf verschiedene Befruchtungen hin, als das hier nicht eine wieder- 
holte Gebnrt in langeren Zwischenzeiten anzunehmen ware.” 
Saks 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. 
77- 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 6tablir 
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.” 
Mey'en 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 subse- 
quently forgotten or overlooked. He says, “Wir haben bei ganz jungen Indivi- 
duen den Verlauf der Blut-bewegung selbst bei 200-maliger Vergrosserung beobachten 
konnen. Der Muttertheil der Placenta hat nur wenige Gefassen 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 Bauchgefiiss ganz in der Nahe 
des Hergens ergiesst. Ein unmittelbares uebergehen der Blutgefasse ausdem Mutter- 
theil in dem F6tus-theil haben wir nicht sehen konnen. Hat der Fdtus die hinlang- 
liche Ausbildung im Leibe der Mutter erreicht, so verwiichst 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 consideration 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 Salpoe 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*. 
In order to avoid the necessity of incessant references to the text, a list of the 
works consulted and alluded to, is here subjoined in chronological order. 
Salpa. — Forskahl. Descriptiones Animalium, 1775. 
Browne. Natural History of Jamaica, 1785. 
* An essential service to zoology ■will be rendered by any one who will revise and critically compare the 
species of the Salpm. At present, they are in a most unedifying state of hopeless confusion. 
