Page:EB1911 - Volume 27.djvu/360

The body appears to be in all cases naked. A differentiation of the peripheral cytoplasm in the form of an ectoplasmic layer has been described in one or two instances, and it seems probable that in most Trypanosomes there is such a layer, although only poorly developed, as a rule, around the body generally. On the other hand, the undulating-membrane is largely if not entirely an ectoplasmic development. This is usually much clearer and more hyaline than the general cytoplasm. In many forms deep-staining grains or granules, of a chromatoid nature and of varying size, are to be seen in the cytoplasm.

Fig. 4.—Representative Amphibian and Piscine Trypanosomes.

A, B, Trypanosoma rotatorium, after Lav. and Mesnil.
C, T. inopinatum, after Serg.
D, T. karyozeukton, after Dutt. and Todd.
E, T. nelspruitense, after Lav. and Mesnil. A B
F, G, Trypanoplasma borreli (living and stained), after Léger. ' C
H, T. cyprini, after Plehn.
J, Trypanosoma soleae, after Lav. and MesniL
K, T. granulosum, after Lav. and Mesnil.
L, T. remaki, var. magna, after Lav. and Mesnil.
h, Clear zone or halo around kineto- a.fl, Anterior flagellum;
nucleus. ffl, Posterior flagellum;
ch, Chain of chromatic rodlets run- .s, Longitudinal striations (myonemes)
ning from trophonucleus to nemes);
kinetonucleus. v, Cytoplasmic vacuole.

In most cases these granules are, if not confined to, chiefly distributed in the posterior (flagellate) half of the body (figs. 3, B, D and E, 4, E and G). In certain Trypanosomes a well-defined, usually oval vacuole is often, though not constantly, to be observed, situated at a varying distance from the anterior end (figs. 3 and C, Cv, 4, F). There is no reason to doubt that this vacuole is a normal cell-constituent, for it has been described in parasites in quite normal surroundings and conditions.

A Trypanosome always possesses two distinct nuclear bodies, one the trophonucleus, regulating the trophic life of the cell, the other, the kinetonucleus, directing its locomotor activities. The recent investigations of Schaudinn and Prowazek (11. c) have shown that, in some forms at any rate, the finer structure and detailed development of the nuclear apparatus is extremely complex. Not only is there an intimate correspondence in this respect between the two principal organelle, but the flagella apparatus itself is really of nuclear origin and remains closely connected with the kinetonucleus (cf. fig. 7). In most cases, however, little-beyond the position and general appearance of the nuclei has been so far made known. The trophonucleus is usually situated somewhere about the middle of the body. The kinetonucleus is typically near the anterior end; but in a few instances it lies more centrally (e.g. T. finopinatam, T. rotaiorium, fig. 4, A–C); in Trypanomorpha it is in the posterior half of the body (fig. 3, E). In certain forms the occurrence of prominent myonemes or muscle-fibrillate has been described, and, moreover, a nuclear origin assigned to them also. In Trypanomorpha they are confined to the undulating-membrane (fig. 3, E), but in other cases—Trypanosoma ziemanni, T. lewisi, T. brucei, and T. soleae-they are arranged laterally, half running down each side of the body (fig. 4, J). In Trypanoplasma borreli there is only a single myoneme on either side.

All Trygagrosomes are capable of binary longitudinal fission, and this appears to be the chief method of multiplication. The division of the nuclear apparatus is the first to take place (fig. 5, A). The kinetonucleus more often leads the way, but sometimes either kinetonucleus or trophonucleus may do so indifferently. The duplication of the flagellum begins at its proximal end, that which is in relation with the kinetonucleus. Until recentl the rocess has been considered as an actual longitudinal splitting of the flagellum, following upon the separation of the two daughter-kineto-1 nuclei. Both Schaudinn (in the case of Trypanomorpha) and Prowazelc (in the case of Trypanosoma lewisi and (T. briucei), have foéxnd, hiowever, tihlatéhe new flagellum is developed quite in epen ently an ai down alongside the old one. It is at present somewhat uncertain, therefore, nn in what cases actual splitting occurs. The same applies equally to the formatlon o the undulating-membrane. If the flagella border splits, the membrane doubtless divides also; but where the flagellum is a new formation the membrane will be too. The division of the cytoplasm in most forms is equal or sub-equal, and two approximately equal dau hter-Trypanosomes result (fig. 5, C§ .- In some instances ag. T. eguinum, T. equfiperdum) the longitudinal fission is apparently multiple, three or even four descenants being produced simultaneously.

(After Lav. and Mesnil.)
Fig. 5.—Stages in Binary Longitudinal Fission of Trypanosoma brucei.

T. lewisi differs from most Trypanosomes in that the cytoplasm divides in a very unequal manner (fig. 6). The process is more comparable to budding, since the larger or parent-individual may produce, successively, more than one “daughter”; moreover, the daughter-individuals may subdivide before separating, the whole family remaining attached by the non-flagellate (anterior) end (fig. 6, F). In this type of division it may be noted that the kinetonucleus comes to lie alongside the trophonucleus, or even asses to the other side of it (i.e. nearer the flagellar end). Easily derivable from this method is the other one characteristic of T. lewisi, viz. segmentation. The chief difference is that in the latter no parent individual is distinguishable, a rosette of many equal daughter parasites being formed.

The small Trypanosomes resulting from either of these modes of division differ from typical adults by their stumpy, pyriform shape, the position of the kinetonucleus near the flagellar end of the body, and the absence, during the first part of their youth, of an undulating-membrane. At this period they have, in fact, what may be termed a “pseudo-Herpetomonadine” aspect. These young individuals can themselves multiply by equal binary fission, giving