fertilization of the queen, by direct means—they prevent them from eating the honey and drive them from the hive, so that they die of hunger[29]. We must also look upon death which immediately, or very quickly, follows upon the deposition of eggs as death by sudden shock. The females of certain species of _Psychidae_, when they reproduce sexually, may remain alive for more than a week waiting for a male: after fertilization, however, they lay their eggs and die, while the parthenogenetic females of the same species lay their eggs and die immediately after leaving the cocoon; so that while the former live for many days, the latter do not last for more than twenty-four hours. ‘The parthenogenetic form of _Solenobia triquetrella_, soon after emergence, lays all her eggs together in the empty case, becomes much shrunken, and dies in a few hours.’ (Letter from Dr. Speyer, Rhoden.) Note 10. Intermingling during the Fission of Unicellular Organisms[30]. Fission is quite symmetrical in _Amoebae_, so that it is impossible to recognise mother and daughter in the two resulting organisms. But in _Euglypha_ and allied forms the existence of a shell introduces a distinguishing mark by which it is possible to discriminate between the products of fission; so that the offspring can be differentiated from the parent. The parent organism, before division, builds the parts of the shell for the daughter form. These parts are arranged on the surface of that part of the protoplasm, external to the old shell, which will be subsequently separated as the daughter-cell. On this part the spicules are arranged and unite to form the new shell. The division of the nucleus takes place after that of the protoplasm, so that the daughter-cell is for some time without a nucleus. Although we can in this species recognise the daughter-cell for some time after separation from the parent by the greater transparency of its younger shell, it is nevertheless impossible to admit that the characteristics of the two animals are in any way different, for just before the separation of the two individuals a circulation of the protoplasm through both shells takes place after the manner described in the text, and there is therefore a complete intermingling of the substance of the two bodies. The difference between the products is even greater after transverse fission of the _Infusoria_, for a new anus must be formed at the anterior part and a new mouth posteriorly. It is not known whether any circulation of the protoplasm takes place, as in _Euglypha_. But even if this does not occur, there is no reason for believing that the two products of division possess a different duration of life.