Lectures on the comparative anatomy and physiology of the invertebrate animals : delivered at the Royal College of Surgeons . to regulate the actions of the muscles of the terminal claspers byw^iicli the hermit keeps firm hold of the central pillar of his bor-rowed cell. The general progress of the development of the nervous system inthe Crustacea has been, as we have seen, attended with increasedsize, and diminished numbers of its central or ganglionic divisions of each pair of ganglia first coalesce by transverseapproximation : distinct pairs of ganglia approximate longitudinally,
Lectures on the comparative anatomy and physiology of the invertebrate animals : delivered at the Royal College of Surgeons . to regulate the actions of the muscles of the terminal claspers byw^iicli the hermit keeps firm hold of the central pillar of his bor-rowed cell. The general progress of the development of the nervous system inthe Crustacea has been, as we have seen, attended with increasedsize, and diminished numbers of its central or ganglionic divisions of each pair of ganglia first coalesce by transverseapproximation : distinct pairs of ganglia approximate longitudinally,conjoining as usual from behind forwards: confluent groups ofganp^lia are next found in definite parts of the body, as on the thoraxof those species which have special developments and uses for par-ticular legs. In the crab, in which the general form of the body * Broderip, Zool. Journ. vol. iv. p. 200. CRUSTACEA. 309 attains most compactness {^fig. 131.), the ventral nervous trunksare concentrated into one large oval ganglion (^), from which thenerves radiate to all parts of the trunk, the legs, and the short tail. 131. This condition of the nervous system has been described by Cuvierin the common crab, and is illustrated by Mr. Swans dissections,from which his beautiful plates have been taken.* The correspond-ing structure of the nervous system is also well displayed by Audouinand Edwards in Maia. An analogous concentration, but not ahomologous one, obtains in Limuhis. Here the nervous substance ischiefly massed round the oesophagus, the fore part of the ringexpanding into a pair of ganglions from which the nerves are sent oifto the small median and large lateral eyes : the nerves to the latterare of great length, wind round the anterior apodemata, and bendback to their termination, breaking up into a fasciculus of minutefilaments before penetrating the large compound eye. Two stomato-gastric nerves arise from the upper and fore part of the ring. Fromthe under surface of the
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Keywords: ., bookauthorowenrichard18041892, bookcentury1800, bookdecade1850
