. Concerning evolution. Evolution. FIGURE NO. 6 AMPHIOXUS OR THE LANCELET Near the beginning of the Vertebrate or Chordate series, there is a class (Cephalochorda) of very primi- tive animals—the lancelets. There are several different kinds, and, like many old-fashioned types, they have a wide geographical distribution. They are found in many seas, spending much of their life buried in the fine sand, the only part protruding being the ciliated cirri (C) around the mouth. The cilia waft in micro- scopic organisms. At times the lancelets bestir them- selves and swim with an undulatory movement i
. Concerning evolution. Evolution. FIGURE NO. 6 AMPHIOXUS OR THE LANCELET Near the beginning of the Vertebrate or Chordate series, there is a class (Cephalochorda) of very primi- tive animals—the lancelets. There are several different kinds, and, like many old-fashioned types, they have a wide geographical distribution. They are found in many seas, spending much of their life buried in the fine sand, the only part protruding being the ciliated cirri (C) around the mouth. The cilia waft in micro- scopic organisms. At times the lancelets bestir them- selves and swim with an undulatory movement in the water, utilizing their 62 or so muscle-segments or myo- tomes (MY). They have the following Vertebrate characters:—a dorsal nerve cord (spinal cord), a dor- sal supporting axis or notochord (N), numerous gill- slits, a segmented body (MY), numerous kidney-tubes or nephridia. But they are in many respects primitive, , in having no skull, no jaws, no limbs, no brain, no heart. There are 26 pairs of reproductive organs or gonads (G). AT is the breathing aperture or atrio- pore; CF, the caudal fin. 62. 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 Thomson, J. Arthur (John Arthur), 1861-1933; Dwight Harrington Terry Foundation. New Haven, Yale University Press; [etc. , etc. ]
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Keywords: ., bookauthorthomsonjarthurjohnart, bookcentury1900, bookdecade1920
