Cestodes Sentence Examples
The remarkable life-history of one species, Linguatula taenioides, has been worked out in detail and presents a close analogy to that of some Cestodes.
In contrast to these segmented or " merozoic " Cestodes, a few primitive forms have preserved a unisegmental' character and form the Monozoa or Cestodaria.
We may therefore divide Cestodes into the Monozoa and the Merozoa.
Archigetes and Caryophyllaeus are the only Cestodes that become fully differentiated in an invertebrate host.
The Cestodes of Elasmobranch fish offer more convincing examples of independent growth of the proglottides, for these are often set free with only the male organs developed, and each attains twice the size of the parental strobila.Advertisement
But whilst in Trematoda a digestive sac is invariably present except in the sporocyst larval stage, the Cestodes possess no trace of this organ at any stage of their development.
The concentration of nervous matter and ganglionic substance at the oral end of Trematodes is equivalent to the " brain " of the Planarians, but the similar thickening in the scolex of Cestodes is by no means so certainly to be called by that name.
Those Cestodes which possess no very distinct organ of attachment (such, for example, as Gyrocotyle) have no distinct ganglionic thickening more pronounced at one end of the body than at the other; and as these are forms which have retained more primitive features than the rest, and show closer affinity to the Trematodes, it seems highly probable that the complicated nervous thickening found in the scolex, and often compared with the " brain " of other Platyelmia, is a structure sui generis developed within the limits of the sub-class.
The power of reparation, so conspicuous a feature of Turbellarians, is slight or absent in Cestodes.
The life-history of Cestodes consists of larval and adult stages, which are usually passed through in different hosts.Advertisement
The peculiar feature of the larval history of Cestodes is the development in most cases of a cyst or hydatid on the inner wall of which the scolex is formed by invagination.
Such is the general history of Cestodes whose intermediate host is an Invertebrate.
It is generally admitted that Cestodes,.
The fact of this increased leucocytic activity during the early stages, or the whole course of infection by Cestodes, is indirect proof that these parasites do normally discharge toxic substances into their hosts.
Table of Cestodes found in Man Literature.Advertisement
In Distomum acanthocephalum the cuticle forms circlets of large and small hooks at the anterior end, somewhat as in Cestodes.
From these are given off at irregular intervals short lateral branches, each of which terminates in a flame-cell (f) precisely similar in structure to the flame-cells found in Planarians, Trematodes and Cestodes; here as there the question whether they are open to the body cavity or not must probably be answered in the negative.
The Planarians are free-living animals, the Trematodes are parasitic upon and within animals, and the Cestodes are wholly endoparasitic.
Within this muscular tube lies a parenchymatous tissue which may be uniform (Cestodes) or differentiated into a central or digestive, and a peripheral portion (some Turbellaria), or finally the central portion becomes tubular and forms the digestive sac (Trematodes), while the peripheral portion is separated from it by a space lined in some forms by a flattened epithelium (most Planarians).
The Cestodes, however, are connected by no such intermediate forms with the other Platyelmia.Advertisement
The Monozoa are unsegmented; the Ligulidce have segmented gonads and gonopores without any trace of somatic metamerization except secondary excretory pores in addition to the usual terminal one; the remaining Cestodes are unisegmental only in their larval stage, and all of them show in their later stages repetition of the reproductive organs and of the musculature.
The chief difference between the reproductive organs of the two classes is the presence in Cestodes of a separate vagina and uterus, each of which opens in some families to the exterior by an independent pore.
The vagina of Cestodes is undoubtedly comparable with the so-called " uterus " of Trematodes, but the nature of the Cestode uterus is not so clear.
It has been compared with the canal of Laurer of Trematodes (the vitello-intestinal duct of the ectoparasitic flukes), but if we take the more primitive Cestodes, and especially Aniphilina, into consideration we find that they possess, in addition to the uterus, an anterior vagina (usually present in Cestodes) and a posterior one.
In the Cestodes the vagina is present (V); the canal of Laurer (LC) is now vestigial (present in Caryophyllaeus as the posterior vagina).Advertisement
The repetition of the genitalia is the real mark of the Cestodes, and we can trace the independence of the somatic from the gonidial metamerism in such forms as Triaenophorus and others.
The loss of nutrient fluid caused by the presence of intestinal Cestodes is probably slight, indeed, the sharper appetite that accompanies their presence may be the means of fully compensating for it.
The so-called flatworms (Platyelmia, q.v.), including the Planarians, Flukes (see Trematodes), Cestodes (see Tapeworm) and the curious Mesozoa, are no doubt related.