. A text-book of invertebrate morphology. Invertebrates. TYPE ANNELIDA. 249 The only sense-organs whicli have been described are a pair of ciliated depressions lying one on each side in the concavity of the lophophore ; no definite statement can be made as to their function. A single pair of nephridia is present, opening into the posterior chamber of the coelom by funnel-like mouths, and ,to the exterior on each side of the anus. They serve not only for excretion, but also as ducts for the reproductive elements. The various species of PTioronis, with the possible exception of P. architecta, ar
. A text-book of invertebrate morphology. Invertebrates. TYPE ANNELIDA. 249 The only sense-organs whicli have been described are a pair of ciliated depressions lying one on each side in the concavity of the lophophore ; no definite statement can be made as to their function. A single pair of nephridia is present, opening into the posterior chamber of the coelom by funnel-like mouths, and ,to the exterior on each side of the anus. They serve not only for excretion, but also as ducts for the reproductive elements. The various species of PTioronis, with the possible exception of P. architecta, are hermaphrodite, the ova and spermatozoa developing from cells of the peritoneum lying in the vicinity of the pouched longitudinal blood-vessel. They are shed from their place of formation into the coelomic cavity and thence pass to the exterior through the Fig. 113.—Metamorphosis of Actinotroaha (after Metschnikofp from Balfour). in = invagination. Development of the PJioronidce.—In their development the various species of Phoronis so far as known undergo a very remarkable metamorphosis. The larva which develops from the ovum is known as Actinotrocha (Fig. 113, A) and is a some- what elongated structure possessing at the anterior end a large hood which overhangs the mouth, its edge bearing. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original McMurrich, J. Playfair (James Playfair), 1859-1939. New York, H. Holt and Company
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