An elementary text-book of biology, comprising vegetable and animal morphology and physiology / by J.R. Ainsworth Davis.

  • James Richard Ainsworth-Davis
Date:
1893
Catalogue details

Licence: Public Domain Mark

Credit: An elementary text-book of biology, comprising vegetable and animal morphology and physiology / by J.R. Ainsworth Davis. Source: Wellcome Collection.

    34/460 (page 18)
    firm cuticle, within which is a well-marked ectosarc or cortical layer, in which an appearance of longitudinal striation may be observed, probably due to an internal fluting, as in Vorticella. AVorm-like movements can be performed by the contraction of this layer. Within the ectosarc is a more fluid endosarc, and there is a large nucleus at one end. There is no contractile vacuole, which is not surprising when the sluggish nature and consequently slow katabolism of the animal is considered. Monocystis undergoes encystment as a regular part of its life- history, and this is usually preceded b}^ the conjugation of two individuals, which come into contact by their anterior ends, some- times fuse, but in any case assume a spherical form and become surrounded by a firm cyst, said to be formed from the cuticle and an altered part of the underlying protoplasm. The contents of the cyst now break up into a large number of spindle-shaped s})ores (pseudonavicellse) invested in firm envelopes, and then, by a process of division, eight nucleated sickle-shaped cells (falciform young) are formed within each spore, a small part of the proto- plasm, however, being left unused (residual core). The falciform young are ultimately liberated by rupture of the cyst and the spore-envelopes. They are capable of movement by alternate l)ending and straightening, and make their way into those cells (spermatospores) from which the male sex-cells of the earthworm are developed, thus becoming intracellular parasites. After a time they quit these cells and gradually assume the adult form. Another common kind of Gregarine is Gregarina (Clepsidrina) blattarum, found in the intestine of the cockroach. A mature individual, when young, possesses an elongated tapering bod}^ (Fig. 3), divided into three regions, (a) an anterior epimerite (‘‘cap”), provided with hook-like cuticular processes, and passing into (b) a protomerite, separated by a transverse septum of ecto- sarc from (c) a much larger deutomerite, in which the nucleus is contained. These regions are probably not distinct cells, but merel}^ parts of one cell. Sooner or later the epimerite is thrown oft'. Two individuals unite, the anterior end of one being opposite the ])Osterior end of the other, and a complicated cyst is secreted, consisting of a number of firm layers with an external gelatinous investment. Repeated nuclear division presumably takes place, and a considerable immber of barrel-shaped spores are foi’ined