258 LILIAN SHELDON. 



EXPLANATION OF PLATES XXII, XXIII, XXIV, 

 XXV and XXVI, 



Illustrating Lilian Sheldon's paper " On the Development of 

 Peripatus novse-zealandise." 



List of Reference Letters. 



an. Anus. Ap. Appendage. At. Antenna, br. Brain. Cer. Com. Cerebral 

 commissure. Ch. Chorion. Ec. Ectoderm. End. Endoderm. L. S. Leg 

 portion of somite. M. Mouth. 3Ies. Mesoblast. n. Nucleus, n. d. Ne- 

 phridial duct. n. s. Nerve cord. Ph. Pharynx. Pm. Protoplasm surround- 

 ing nucleus. Pm. A. Protoplasmic area. Pm. S. Protoplasmic segments. 

 p. Cavity in proliferating mass of nuclei, p. n. Proliferating mass of nuclei. 

 p. 0. 1. Prseoral lobe. post. Em. Posterior end of embryo, pr. g. Primitive 

 groove, pr. st. Primitive streak, p. y. Peripheral yolk. S. Somite. Sep. 

 Septum between the two cavities. So. Somatic wall of somite. Sp. Splanchnic 

 wall of somite. St. Stomodaeal invagination. V. m. Vitelline membrane. 

 Y. Yolk in the embryo. T. S. Yolk segments. 



All the figures, except Nos. 23, 24, 25 and 26, were drawn with Zeiss's 

 camera lucida ; the power under which it was drawn is stated after the 

 description of each figure. 



I'iG. 1. — Transverse section through an unsegmented ovum, in which the 

 nucleus is at some little distance from the periphery. The yolk is unsegmented. 

 n. Nucleus. T. Yolk. Pm. Protoplasm surrounding the nucleus. Oc. 2, 

 obj. B. 



Fig. 2. — Section through a small portion of an unsegmented ovum, showing 

 the nucleus situated close to the periphery, n. Nucleus. Pm. Protoplasm 

 surrounding the nucleus. Y. Yolk. V. m. Vitelline membrane. Ch. Chorion. 

 Oc. 2, obj. D. 



Figs. 3 a and 3 b. — Transverse sections through an ovum, in which two 

 nuclei are present, and in which the yolk has not begun to segment. 



Fig. 3 a passes through one nucleus, which is situated at the periphery of 



the egg, and has a lobed form. 

 Fig. 3 h passes through the other nucleus, which is at the same pole as 

 that in Fig. Sos, but lies deeper in the egg. It is in a state of division, 

 the section passing transversely through the spindle, n. Nucleus. 

 Pm, Protoplasm surrounding the nucleus. Y. Yolk. Oc. 2, obj. B. 



