[3] I find, in Milne-Edwards’ ‘Leçons sur la Physiol. et l’Anat. comp.’ 3 page 197, the statement that, according to Frey and Leuckart, the heart of _Caprella linearis_ possesses _five_ pairs of fissures. I have examined perfectly transparent young Caprellæ (probably the young of Caprella attenuata, Dana, with which they occurred), but can only find the usual three pairs. CHAPTER VII. STRUCTURE OF THE HEART IN THE EDRIOPHTHALMA. Let us first glance over the extant facts. Among the Stalk-eyed Crustacea (_Podophthalma_) we know only a very few species which quit the egg in the form of their parents, with the full number of well-jointed appendages to the body. This is the case according to Rathke[1] in the European fresh-water Crayfish, and according to Westwood in a West Indian Land Crab (_Gecarcinus_). Both exceptions therefore belong to the small number of Stalk-eyed Crustacea which live in fresh water or on the land, as indeed in many other cases fresh-water and terrestrial animals undergo no transformations, whilst their allies in the sea have a metamorphosis to undergo. I may refer to the Earthworms and Leeches among the Annelida, which chiefly belong to the land and to fresh water,—to the _Planariæ_ of the fresh waters and the _Tetrastemma_ of the sparingly saline Baltic among the Turbellaria,—to the Pulmonate Gasteropoda, and to the Branchiferous Gasteropoda of the fresh waters, the young of which (according to Troschel’s ‘Handb. der Zoologie’) have no ciliated buccal lobes, although such organs are possessed by the very similar Periwinkles (_Littorina_). All the marine forms of this section appear to be subject to a more or less considerable metamorphosis. This appears to be only inconsiderable in the common Lobster, the young of which, according to Van Beneden, are distinguished from the adult animal, by having their feet furnished, like those of _Mysis,_ with a swimming branch projecting freely outwards. From a figure given by Couch the appendages of the abdomen and tail also appear to be wanting.