. A text-book of invertebrate morphology. Invertebrates. 602 INVERTEBRATE MORPHOLOGY. ones are in the younger stages of development, a tonguelike valve later growing down from the dorsal border of the pore and giving it its U-shaped form. Water flows in at the mouth and passes out through the branchial slits, which thus pos- sess a respiratory function. A few of the anterior slits open. Fig. 374.—Balanoglossus Kowalewskii (after Mdjot from Spkngel). br = branchial slit. c = collar. pr = proboscis. externally into the atrium, being covered over by the back- wardly-projecting atrial folds of the
. A text-book of invertebrate morphology. Invertebrates. 602 INVERTEBRATE MORPHOLOGY. ones are in the younger stages of development, a tonguelike valve later growing down from the dorsal border of the pore and giving it its U-shaped form. Water flows in at the mouth and passes out through the branchial slits, which thus pos- sess a respiratory function. A few of the anterior slits open. Fig. 374.—Balanoglossus Kowalewskii (after Mdjot from Spkngel). br = branchial slit. c = collar. pr = proboscis. externally into the atrium, being covered over by the back- wardly-projecting atrial folds of the collar, but the majority are quite uncovered and are plainly visible from the exterior. ' The ectoderm contains numerous mucous glands and is ciliated throughout, no external cuticle or " house," such as occurs in the Pterobranchia, being developed. Below it rests upon a thin basement-membrane. The coelom is clearly marked out, and consists of three portions completely separated from one another and corre- sponding to the three body regions. The proboscis-coelom (Fig. 275, A, pc) is, in its anterior portion, a simple unpaired cavity lined with delicate cells and traversed by circular and longitudinal (Zm) muscle-fibres. Posteriorly it is prolonged into two horns between which lies a mass of tissue consisting. 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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