JOURNAL OF MICROSCOPICAL SCIENCE. 



EXPLANATIONS OF PLATE XII— XV. 



Illustrating C. O. Whitman's paper on " The Embryology 

 of Clepsine." 



(All the figures are outlined with the camera lucida.) 

 a, b, c. Permanent blastonieres. ar. Anal ring of dorsal blood-vessel. 

 b.cal. Base of calotte, cp. Central part of polar area (amphiaster). eg. 

 Cerebral ganglia. c. Caca of stomach. c«l. Calotte. CO. Cephalic 

 branch, d. Terminal disc. d.t. Dorsal trunk, ea. External orifice of 

 segmental organ. Ent. Entoderm. Ep Epidermis. /'./;«. Eemale pro- 

 nucleus, f-pnl. female pronucleolus. gh. Germ-bands, ia. Internal ori- 

 fice of segmental organ, id. Diverticula of intesliue. i. Intestine, m. 

 Mesoderm. m.Fn. Male pronucleus. m.PiiL Male pronucleolus. Med.S 

 Median sinus, ms. Marginal sinus, n. Nerve-cells, o. (Esophagus, oa. 

 Pliaryngeal atrium, o.c. Pliaryngeal clefts. P. Pharynx. Pa. Polar area 

 of amphiaster. Pa. Pharyngeal a|i€iture (moutii, figs. 37 — 49). Pb. 

 Pharyngeal branch. Pf. Polar fitrure. Pg. Polar globules. Pgr. Primi- 

 tive groove. Pr. Polar ring (upper). Pr. Polar ring (lower). Pz. Pro- 

 toplasm-zones. *. Segment-cells. Seg.c. Segmentation cavity. Seg.O. 

 Segmental organ. Sep. Septa. SO.G. SubcBsophageal ganglia. St. Sto- 

 mach, t.h g. Terminal body-ganglia, vt. Ventral trunk, x ^ xy. Meso- 

 blasts. x^ — x^. Neuroblasts, z. Problematic cells. 



PLATE XIL 



(Figs. 1 — 55 magnified about 25 diameters.) 



Figs. 1 — 7- — A peristaltic constriction, resembling the first cleavage 

 constriction, passes from the middle of the t^'g (fi::. 2) towards the polar 

 figure (/y*, and is followed by the extrusion of the first polar globule (fig. 

 ''i",Pg). Time from fi.'. 1 to fig. 7, 10—15 mim 



EiG. 8. — Form of egg after appearance of the second pol. globule. (1 h. 

 25 min. after deposit.) 



Fig. 9. — First ring appears around the shaded area of fig. 8. (1 h. 30 

 min.) 



Fig. 10. — Second ring [Pr) appears, aud at about the same time ring- 

 rays from the upper ring. (1 h. 35 min.) 



Fig. 11. — The calotte much reduced \<-al). The lower ring-substance 

 covers the aboral pole in the form of a disc. Itajs of the ring-substance 

 seen at bolli j)oles. ( 



Fig. 12. — Just before the appearance of the cleavage furrow. Calotte 

 has approached one side of the ring, aud the rays have nearly disappeared. 

 (2 h. 4.5 min.) 



Figs. 13 and 14. — Two views of the same, egg as the cleavage begins. 

 Pr is reduced to a n;ere point. Pr has assumed a cresceutic shape. 

 (3 h.) 



Fig. 15. — The first meridional cleavage completed. The cleavage walls 

 close up sooner on tlie upper than on the lower pole. (3 h. 30 min.) 



Fig. 16. — Thirty minutes later. Seeu from above. Pr begins to dis- 

 appear. 



