EXPLANATION OF PLATES VI, VII, VIII, AND IX. 



Fig. 38. Through the dorsal division of somite 4 and the hind part of the 

 ventral division of somite 3, the opening between the tvpo parts (in- 

 ternal vesicular portion, /. s. v. 3, and tubular portion, /. s. t. 3) of which 

 are shown, m. I. Muscles of internal projection of jaws. 



Fig. 38 a. One side of a section, a little behind fig. 38, to show the com- 

 mencing salivary gland (*«■/. ^.). Zeiss's D, oc. 2. Reduced^. 



Fig. 39. Between the oral papilla and first leg. 



Fig. 40. Through the third leg, to show the ventral division of the sixth 

 somite. The tubular portion of this (nephridiura of third leg) is a 

 straight tube (the lumen is not distinct, but this was probably due to 

 the contraction of the specimen), opening externally at o. n. 6, and in- 

 ternally into the internal vesicular portion {I. s. v. 6). 



Fig. 41. Through the twentieth somite, in the region of the generative cells. 

 The differentiation of the various divisions of the body cavity has hardly 

 reached this part of the body, b. k., d.pc, 6. be'., being only present in 

 a rudimentary form. The endoderm is slightly shrivelled up. The 

 generative nuclei are still in the endoderm, though some of them project 

 into the body cavity. Zeiss's D, oc. 2. Reduced J. 



Fig. 42. Through the rectum and anal papillae (rudimentary eighteenth leg) . 

 The dorsal and ventral divisions of the somite are in communication. 



Figs. 43 — 46 are from old embryos of Stage f. Zeiss's D, oc. 2. Re- 

 duced i. 



Fig. 43. Througii the seventeenth somite, to show the dorsal division of the 

 somite {d. s.), which may now be called the generative gland. The gut 

 has separated from the latter, so that the two divisions of the part of 

 the body cavity marked b. be', communicate. The dorsal part of the 

 section only is drawn. 



Fig. 44. Through the anal papilla (rudimentary eighteenth leg) and twenty- 

 first somite. The two parts of the somite are in communication, and 

 the ventral has almost acquired an opening to the exterior. This 

 opening will be the generative opening. 



Figs. 45 and 46. — Dorsal parts of two transverse sections from the middle 

 region of the body in front of the generative region ; 46 is the anterior. 

 In 45 the dorsal division of the somite {d. s.) is not yet obliterated ; in 

 46 it has entirely vanished, and is represented only by the thickened 

 layer of cells which form the ventral wall of the heart. 



Figs. 47 and 48. — Through the generative organs of an embryo of Stage g, 

 in the region where they are detached from the pericardial floor. Zeiss's F, 

 oc. 2. 



Fig. 49.^ — Longitudinal vertical section through the anterior part of the 

 body of an embryo of Stage r. Reduced 3. 



Fig. 50. — One side of a transverse section through a young embryo of Stage 



