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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated.1900 Excerpt: ... called Ersatz cells, destined to give rise to epithelium, but still capable of being transformed into neuroblasts. After being formed in this ventral position the nerve-cords migrate upward along either side of the body to their final normal situation, carrying with them a thick covering of the neuroblast cells (fig. 22). As soon as the nerve-cords leave the ridges, gland cells begin to appear in the epiblast covering the latter, and it becomes in all respects like that on the outside of the grooves. The grooves then disappear, and leave a smooth epithelial surface. The new nerve, therefore, is in no respect an outgrowth from the old one, but results from a new growth of cells which are entirely independent of the old nervous system. It hardly seems reasonable that this Nemertean in its embryology should derive its nervous system from mesoblast when in regenerating lost parts it shows such a distinctively epiblastic origin. Larval Development. Sexual Organs. The sexes are distinct as in most Nemerteans. There is no perceptible difference in external form or size, but in the breeding season there is a difference in colour, due to the sexual products which show through the body-wall. The male then appears cream-coloured, while the female is greyish red, turning to a light chocolate-brown in many cases. This difference is clearly seen in the male and female photographed in fig. 3, the latter being much the darker of the two. In regard to the original formation of the genital pouches, nothing can be offered in the present paper, since the development is not followed that far. Hubrecht considers (26) that they arise.is invaginations of the ectoderm in Lineus, but Burger's comment seems far more probable. He says (13, p. 480), " I have not been able to decide upo...
