410 T^essrs. iCorcn and Danielssen on the 



mass, and acquires a rolled-up form^ for its margins are curved 

 inwards towards the plane. When we examine it superficially 

 in this state, we find that it has some resemblance to a canal. 

 But on observing it attentively, we soon recover the right road. 

 In following the development of the foot, we see changes of 

 form and structure, as well as the auditory organs at its base. 

 If the English physiologist had done this, he would have been 

 convinced that at first there was no mouth or oesophagus, and 

 that therefore there could be no question of devouring the con- 

 glomerated eggs. But he would also have been able to ascertain 

 that a group of eggs in different stages of segmentation is sur- 

 rounded by a membrane, and that organization commences 

 subsequently. It is curious, however, that Dr. Carpenter did 

 not inquire what became of the foot of his embryos, as he is 

 perfectly aware that this organ makes its appearance very early 

 in the Mollusca, while he only speaks of the foot when it is com- 

 pletely developed, both as regards form and structure. But he 

 observed a mouth and oesophagus, and full of the idea of the 

 formation of these organs, he completely forgot the foot, which, 

 however, is of considerable importance in the Mollusca.. 



In spite of all this, Dr. Carpenter would perhaps have avoided 

 these errors if he had employed an intense light from above, for 

 he would then have seen how the eggs in different states of 

 segmentation were placed in layers, like a heap of balls, in the 

 interior of the membrane, of which we have already spoken 

 sufficiently (PI. XVII. fig, 2). If he had crushed an embryo 

 of this kind, he would also have been convinced that the entire 

 eggs were placed one upon the other, as they occur in the con- 

 glomerate before the envelopes of the embryos are formed. 

 With an ordinary light, he would have observed in a mass of 

 embryos, towards the inner surface of the membrane, entire 

 eggs, which allowed their spheres of segmentation to be seen 

 distinctly. But this could not be the case if Dr. Carpenter 

 was right, as he does not believe that these little creatures 

 swallowed entire eggs; this, however, has also escaped him. 

 When he states that he has seen how the embryos eat and 

 swallow the vitelline mass, this is an illusion, for it sometimes 

 happens that some vitelline segments attach themselves to the 

 foot itself, long after the embryo has detached itself from the 

 conglomerate; but, far from swallowing them, it endeavours 

 with all its power to get rid of them, in which it most frequently 

 succeeds. 



Dr. Carpenter also indicates that we have deceived ourselves 

 with regard to the development of the heart, and states that we 

 have taken the contractile vesicle (kidney) for the heart. He 

 asserts that the latter is not formed until after the contractile 



