. Comparative anatomy and physiology. Chap. III.] ENTER OPNE us TI. combine with them the knowledge of the fact that, in certain Nemertines, the nerve cords, instead of lying at the sides of the body, tend to take up a dorsal posi- tion. Whether or no Hubrecht is right in regarding the Nemertinea as giving us indications of where to look for the ancestral form of the Chordata, it is clear that we must sharply distinguish them from the group of the Platyhelminthes, with which they have. Fig. 42.—A, Diagram to show the relation of the proboscis (pbs) to the surface of the body and to the sheath
. Comparative anatomy and physiology. Chap. III.] ENTER OPNE us TI. combine with them the knowledge of the fact that, in certain Nemertines, the nerve cords, instead of lying at the sides of the body, tend to take up a dorsal posi- tion. Whether or no Hubrecht is right in regarding the Nemertinea as giving us indications of where to look for the ancestral form of the Chordata, it is clear that we must sharply distinguish them from the group of the Platyhelminthes, with which they have. Fig. 42.—A, Diagram to show the relation of the proboscis (pbs) to the surface of the body and to the sheath of the proboscis (pbs), in the Nemertinea; (B) diagram of Petromyzon (the lamprey) showing the hypophysis cerebri (hyp) ; the chorda dorsalis (ch); the mouth (m); and the anus (a). (After A. A. W. Hubrecht.) been hitherto very closely associated. Linens, Cari- nella, Polia, are examples of this group. So, again, in another group of " worms," the Euteropiieiisti, the sole representative of which is the remarkable Balanoglossus (Fig. 43), the anterior portion of the eiiteron divides into a ventral and a dorsal portion ; the former retains its nutrient office, but the latter has chitinous lamellae developed in its walls ; between these clefts (br) appear, which finally open on the surface of the body ; blood-vessels are richly distributed to the walls of the arches, and the water taken in by the mouth passes through the clefts to the exterior. In Balanoglossus, therefore, just as. 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 Bell, F. J. (Francis Jeffrey), 1855-1924. London, Cassell
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