The fecundity of Mulattoes is not touched in this passage, not having been the subject of discussion. The question merely was whether the prevalent opinion, that intermixture of improved races physically, intellectually, and morally, was in accordance with well observed facts. Hence, M. Boudin confined his observations to the limited intelligence exhibited by the Mulattoes issued from the union of the Dutch of Java with the Malay women. But in his _Treatise on Medical Geography_,[36] he expresses, with regard to the Mulattoes, an opinion that they are not productive beyond the third generation. This fact, announced by Dr. Yvan, which is confirmed by other testimonies, has not been contested. Waitz borrows from Graf Görtz some particulars which are not without interest. “The Lipplappen,” he says (this is the name of the Mulattoes of Java), “do not breed beyond the third generation. Flabby and weakly, they become developed up to the fifteenth year, when the development is arrested. At the third generation, girls only are born, which are sterile.[37] This phase of sterility is very curious, and deserves well the attention of physiologists.” It is, however, necessary to inquire whether the sterility of the Lipplappen depends upon intermixture or upon other causes. The climate of the islands of the Sunda straits is very injurious to Europeans. The Dutch do not perpetuate their race at Batavia; and even without intermarrying with the natives they become sometimes sterile at the second generation.[38] The sterility of the natives may, then, be attributed to the climate. These results, moreover prove, from a verbal communication of Dr. Yvan to M. de Quatrefages, that in other Dutch colonies of the Great Indian Archipelago, the Mulattoes are prolific.[39] It is thus not demonstrated that the sterility of the Lipplappen is the result of their hybridity.