xlii EXPLANATION OF ri.ATES 29, 30. 



No. 3. Penultimate section, in which the Miillerian duct is visible ; it is separated 

 by three sections from No. 2. 



No. 4. Last section in which any trace of the Miillerian duct is visible ; the 

 lumen, which was visible in the previous section, is now absent. 



No. 5. No trace of Miillerian duct. Nos. 3, 4, and 5 are consecutive sections. 



Fir.. K. Section through the hind end of the abdominal opening of the Miillerian 

 duct of a chick of 123 hours. Zeiss C, ocid. 2 (reduced one-third). Il illustrates the 

 peculiar cord connecting the Miillerian and Wolffian ducts. 



EXPLANATION OF PLATE 29. (XIV. p. 644.) 



CoMTLETE List of Reference Letters. 

 am. Amnion. c/i. Notochord. c//. Notochordal thickening of hypoblast. 

 e/i. Epiblast. /ij. Hypoblast, w.^'. Medullary groove. «<•./. Mesoblastic plate. 

 Kt'. Neurenteric canal (blastopore), /ir. Primitive streak. 



Series A. Sections through an embryo shortly after the formation of the medul- 

 lary groove. X 120'. 



Fig. I. .Section through the trunk of the embryo. 

 Figs. 2 — 5. Sections through the neurenteric canal. 



Fig. B. Surface view of a somewhat older embryo than that from which Scries A 

 is taken, x 30. 



.Series B. .Sections through the embryo represented in Fig. B. x 120. 



Fig. I . Section through the trunk of the embryo. 



Figs. 2, 3. Sections through the hind end of the medullary groove. 



Fig. 4. Section through the neurenteric canal. 



Fig. 5. Section through the primitive streak. 



Fig C. Surface view of a somewhat older embryo than thai reiircsentc<l in 

 Fig. B. X 30. 



EXPLANATION OF PLATES 30, 31, 32. (XVII. p. f.6s.) 

 Plate 30. 

 Complete List of Reference Letters. 

 (■//. CheliceraD. (■/;.,?■. Ganglion of chelicercv. r. /. Caudal lobe. /<. r. Primitive 

 cumulus. /(/. Pedipalpi. />r. I. Pra;oral lobe. //'. //-. etc. Provisional ap- 

 pendages. sj>. Spinnerets. .</. Stomodncum. 



I — IV. Ambulatory appcnd.iges. i — 16. Postoral segments. 



Fig. I. Ovum, with primitive cumulus and streak proceeding from it. 



• 'J'hc spaces between the l.^ycrs in these sections are dtie to the action of tlie har(!eiiing rc-nKcnt 



