_Multiplication_ in the vertebrate is brought about by longitudinal division. According to the recent account of division by Miss Robertson, the blepharoplast doubles, then the flagellum splits for the greater part of its length, and the daughter flagella separate, one being shorter than the parent flagellum. The nucleus often shows two well marked dark granules on the membrane at opposite poles, and these appear to act as centrosomes. Nuclear constriction occurs and the halves gradually separate. Finally the two daughter organisms become free, the aflagellar end splitting last. The products of division may be equal or unequal. Repeated division goes on in the general circulation until the blood swarms with parasites. Then the trypanosomes gradually disappear, and a period occurs when it is practically impossible to demonstrate the parasite in the blood. At such a period, trypanosomes can be obtained by puncture of the enlarged lymphatic glands or of the spinal canal, or can be found in the internal organs, more particularly in the spleen, lungs, liver and bone-marrow. In the latter organs, latent bodies are produced (fig. 29, _d_--_f_) which are capable of again becoming flagellates and entering the general circulation. Their formation was described by Fantham (1911).[60] The parasite contracts, the blepharoplast migrates towards the nucleus, a very thin coat differentiates around the two nuclei and a certain amount of cytoplasm, and the parts exterior to the coat disintegrate, leaving a small, oval body behind. Fuller details are given in connection with _T. rhodesiense_. Laveran (1911)[61] considers that latent bodies are “involution” forms, but acknowledges that they can flagellate and become infective in fresh blood. [60] _Proc. Roy. Soc._, B, lxxxiii, p. 212. [61] _C. R. Acad. Sci._, 153, p. 649. No multiplication of the trypanosomes within the cells of the lung, liver or spleen of infected monkeys was found by Miss Robertson in her recent researches. There appear to be negative periods in infected monkeys, since, although trypanosomes may occur in their blood at such times, they are not infective to _Glossina_. _Development in Glossina palpalis._--The principal accounts are those by Sir D. Bruce and his colleagues (1911),[62] and by Miss Robertson[63] (1912), whose results will be followed. According to the latter investigator _T. gambiense_ never enters the body cells of the fly (_G. palpalis_), nor does it penetrate the gut wall into the body cavity. Practically no crithidial stage occurs in the fly’s main gut, but a trypanosome facies is retained therein. [62] _Proc. Roy. Soc._, B, lxxxiii, p. 513. [63] _Proc. Roy. Soc._, B, lxxxvi, p. 66.