. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). 180 IN VERTEBRA TE MORPHOLOQ Y. lit rm ^ <« also found in Mammalia and in exceptional cases in man. A great uniformity of structure exists thvoughout all the species, so that they are all referable to a single genus, Echimrhynclms. The body (Fig. 90) is cylindrical and as a rule not very long, and a marked distinction froni the -Nematodes is found in the retractile proboscis {pr) occurring at the anterior end of the body. It is a cylindrical prolongation of the an
. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). 180 IN VERTEBRA TE MORPHOLOQ Y. lit rm ^ <« also found in Mammalia and in exceptional cases in man. A great uniformity of structure exists thvoughout all the species, so that they are all referable to a single genus, Echimrhynclms. The body (Fig. 90) is cylindrical and as a rule not very long, and a marked distinction froni the -Nematodes is found in the retractile proboscis {pr) occurring at the anterior end of the body. It is a cylindrical prolongation of the anterior portion of the body and is provided M'ith a number of chitinous hooks by means of which it adheres to the intestinal wall of its host. The proboscis may be invagi- nated into a double-walled muscular proboscis-sheath by whose contraction it may again be protruded, a strong retractor muscle, extending from the tip of the proboscis to the base of the sheatli, serving for the invagination ; and from the base of the sheath re- tractor muscles {rm) pass to the body- walls and serve to hold the sheath in position. No traces of a digestive tract occur. The body is covered upon the out- side by a thick cuticle secreted by the subjacent hypodermis, which is a rather Fig. Echinarhyn- thick layer consisting of a protoplasmic ' niatiix in which nuclei are scattered but in which no cell-outlines are to be distinguished. Beneath the cuticle the matrix has a fibrillar character, and near its inner surface it is hollowed out into a network of anastomosing canals of which mention will be made later. Beneath the hypodermis lies a basement-membrane within which are Uvo layers of muscle-cells, having the same thoho-muscular character as those of the Nematodes, the fibres of the external layer having a circular direction, while. g - glands I = leiuiiisciis p = pt'uis. pg = proboscis ganglion pr â = proboscis. nn â retractor muscle. t = Please note that these i
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