. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). h !' I \ 472 INVERTEBRATE the type consists of a siipraoesopliageal ganglionic mass, con- by circumcBsophageal commissures with a chain of ventral ganglia, a pair of ganglia corresponding typically with each segment. In the Insecta (Fig, 228) more especially, however, considerable concentration occurs, a number of the })ostoral ganglia, or, in some cases, all of them, fusing to a single mass. A well-developed stomatogastric or sympathetic nervous sy
. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). h !' I \ 472 INVERTEBRATE the type consists of a siipraoesopliageal ganglionic mass, con- by circumcBsophageal commissures with a chain of ventral ganglia, a pair of ganglia corresponding typically with each segment. In the Insecta (Fig, 228) more especially, however, considerable concentration occurs, a number of the })ostoral ganglia, or, in some cases, all of them, fusing to a single mass. A well-developed stomatogastric or sympathetic nervous system occurs in all forms, arising from the supra- uisophageal ganglionic mass by two trunks, which unite to form a single nerve, passing to the digestive tract, and in some cases provided with ganglionic enlargements both paired and unpaired. Sense-organs of various kinds are well developed in the Tracheata, with the exception of Peripatus, in which the only definite orpaus of special sense are the eyes. In other forms the antenna and other portions of the bodv are pro- vided with hairs connected with nerves and serving as tactile organs, and seta) situated upon the mouth-})arts and associated with peculiar nerve-endings have been supposed to represent organs of taste, and others again, on the antenuje, olfactory organs. Eyes .are very generally present. In Peripidns ami most Myriapoda simple ayes or ocelli are alone present; in l*evipatus they resemble closely in structure the eycK of the Annelids or Mollusca ( Ilalioiis, see Fig. 134), but in the Myriapods and Insects they are usually more complicattnl. Tims in a young larva of AciUm (Fig. 216, A\ a water- beetle, the chitin is thickened to form a cornea (J) whicli lies over a depression of the liy^^oderMiis, the cells at the bottom of which are modified to form a retina, each being contiuuoiiH at its inner end with the optio nerve (7t), while at its outer end it bej-rs a layer of chitin (/). The cells of the lip of tli
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