179 



GERM-LAYERS IN CLEPSINE. 



[No. I. 



EXPLANATION OF PLATE IV. 



Reference Letters. 



a, left macromere. 



b, right macromere. 



c, anterior and median macromere. 

 cl, cephalic lobe. 



ec, ectoderm. 



e», entoderm. 



enp, entoplast. 



ef, epidermal layer. 



;«, mesoderm. 



m\ lateral cell-row. 



nb, teloblasts of the neuronephric 

 stratum. 



«c, nerve-cord, neural cell-rows, neu- 

 roblast. 



nph, nephridial rows. 



p, posterior end of cephalic lobe. 



*, right mesoblast. 



xy, left mesoblast. 



y, yolk. 



Fig. I. C. complanata from Naples. Surface view of germ-bands in an 

 equatorial position. The white blotches in the yolk are entoplasts {enp.) 



X 1 20. 



Fig. 2. C. c<?;«jz>/a«ai'« (Naples) . Transverse section near the middle of the 

 tgg, in a little earlier stage. The contrast in color between the superficial and 

 the deeper cells of the ectoderm has been made too great by the lithographer. 



X 120. 



Fig. 3. C. complanata (Naples). Median sagittal section of the same 

 stage. X 120. 



Fig. 4. Cephalic lobe and underlying yolk, from the same series of sec- 

 tions, but a little to one side of the median plane. X 2S0. 



Fig. 5. An obliquely horizontal section of the same stage, at the level of 

 the arrow 5-5 in Fig. 3. X 120. 



Fig. 6 C. parasita (Cambridge, Mass.). Transverse section of the em- 

 bryo, when the germ-bands are a little more than two-thirds closed. Section 

 is just in front of the unclosed portion of the bands. X 280. 



Fig. 7. From the same series, iust behind the point of closure. 



