72 Miscellaneous. We may therefore conclude that the unpaired eye in all the Crustacea that possess it is composed of three simple eyes, placed anterior to the Drain, with reversed optical bacilli, receiving conduc-tive fibres of the optic nerve upon their outer margin, and brought so close together that their pigmented or choroid layers are combined into a single mass. "We may detect a nearly identical structure of the visual organ in two other groups : — -1. The Cheetognatha, according to M. Hertwig, have absolutely the triple eye of the Crustacea ; but, instead of being median and unpaired, it is repeated on the two sides of the head. 2. Certain Planarians, Dendroccelum lacteum for example, have two paired eyes, which, according to Justus Carriere, have the structure which I adopt for one of the simple eyes united in the median eye of the Crustacea. It is probable that the eye of the Chsetognatha and Crustacea is to be referred back to the type of the Planarians, but that the two former groups have no direct relationship between them. The method of thin sections has revealed to me some other in-teresting peculiarities, which I hope soon to publish in a more extended memoir upon Cyclops. The eye which most nearly approaches that of the Crustacea and Chsetognatha seems to be that of the Planarice. M. Justus Carriere has just published (Arch, fiir mikr. Anat. xx. p. 160) a memoir on the eyes of these very primitive animals ; and, according to his text and figures, it must be assumed that each eye of the Planaria or Dendroccelum represents one of the components of the eye of the Crustacea. It is therefore more rational to refer back the eyes of the Crustacea and Chaetognatha to such a primitive ancestral group as the Turbellaria than to seek direct approximations between the two former groups. — Comptes Bendus, May 22, 1882, p. 1430. Sponges from the Neighbourhood of Boston, U.S. Mr. E. Potts exhibited some fragments of freshwater sponges collected in the Cochituate Aqueduct and sent to him by the Super-intendent of the Boston Waterworks. Alluding to the deleterious effects recently attributed to this sponge, as the cause of the pollu-tion of the Boston water-supply, he said he was not prepared either to affirm or deny it. While he was well aware that a decaying freshwater sponge was one of the foulest things in nature, in his own experience he had never met with it in sufficient quantities, locally, to suppose it capable of tainting, in its decay, millions of gallons of water, as now represented. An examination of the sponge as to its specific relations revealed some peculiar facts. Primarily it was evident that the sponge was much " mixed," the presence of two or more species being very apparent. One of these, with long branching finger-like processes, smooth
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