I HAVE just read with much interest the paper in NATURE by Mr. W. Saville Kent, criticising my friend Carter's article in the “Annals of Natural History” for this month, in which I fully concur. How Mr. Carter can have fallen into such an error, for such I must call it. I cannot imagine, as comparing a group of animals in Botryllus to those sponge cells, even in so highly a developed form as Grantia. For, taking this as the highest known form of sponge animal, it is at most only a monociliated sac, as shown both by Prof. Clark and by Mr. Carter. Now, it is well known to all investigators, and Mr. Carter has shown it himself, that the animals of Botryllus have distinct oral and faecal apertures, whereas the sponge cell, so far as has yet been seen, has only an oral aperture. Again, the Ascidian Botryllus is shown to be far higher in the scale when we come to compare its internal organisation, and not merely to confine ourselves to the sac-like tunic. The discharge of the faecal matter into a common cloacal canal is to me not a sufficient reason for comparing these groups of animals to the sponge animals in Grantia.