. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). 144 INVERTEBRATE MORPHOLOO T. into two limbs wbicli are continued backwards, in some cases giving off secondary branches, to near the posterior end of the body, where they either end blindly or unite together in the middle line (Polystomum) to form a loop. The body is covered by a distinct cuticle secreted by the ectodermal celJK, which in the adult may undergo a con- siderable amount of degeneration, or probably in some cases the cuticle is formed in part by the transf
. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). 144 INVERTEBRATE MORPHOLOO T. into two limbs wbicli are continued backwards, in some cases giving off secondary branches, to near the posterior end of the body, where they either end blindly or unite together in the middle line (Polystomum) to form a loop. The body is covered by a distinct cuticle secreted by the ectodermal celJK, which in the adult may undergo a con- siderable amount of degeneration, or probably in some cases the cuticle is formed in part by the transformation into chitin of the ectoderm. Spiny ele- vations of the cuticle are present in many forms, and the large chitinous hooks which occur in many ectopara- sitic forms are but further develop- ments of these structures. Below the ectoderm lies the usually thin base- ment - membrane, below which again lie the circular and longitudinal pe- Fw. ),nn cyg. ripheral muscle-sheets, and between HOe«^« (from a (IrawitiL' l)y ,1 • , ,. 1 ,, , . the intestine and these muscles is the parenchyma traversed by dorsoventral muscle bundles and ha\ iiig imbedded in it the re])r()ductive and other organs of the body. The nervous system (Fig. 77) con- sists of a transversely elongated gan- glion lying dorsal to the (esopluigus— usually between the bottom of tln' ant(>rior sucker and the i)haryng»'iil bulb. The ganglion is somewhat swollen at each extremity, indicating its origin by the approximation of two ganglionic masses, and from these thickenings nerves arise which \y,\M both forward and backward. The anterior nerves are shoit and slender, and supply the musculature of the anterior sucker and the sides of the anterior end of the body, whilf the })osterior nerves are much sti'onger and longer and varv from two to six in number ; in the latter case four run aloni^. C Lan(!Knhkcki. as = iiiitcrioi' sucker il = iiiU'stine. ov = ovary p = reproductive orilico. ph = iiliii
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1896
