PLATE XXVII 



Fig. i. The diploid set of chromosomes from the saccus ectoderm. 

 Late prophase. F.W.A., thionin. Scale I 5 *" I 



Fig. 2. The codon ectoderm of P/rysa/ja, showingpartofthenerveplexus. 

 Formaldehyde-sublimate, Holmes's silver method. Scale I 25/t 



Fig. 3. Frayed edge of mesogloea from the saccus, showing criss-cross 

 laminae. Helly, iron haematoxylin. Scale 1 "jgif I 



Fig. 4. Gelatin section through the codon, near the base of some 

 appendages. ' Bridge cells ' cross the mesogloea from the endo- 

 derm (bottom) to the ectoderm (top right). F.W.A., Mayer's 

 haemalum. Scale ' SO/* I 



Fig. 5. Surface view of the codon ectoderm, in a region where the 

 cuticle is partly disintegrated. Strands of cuticular material are 

 seen running obliquely down from the underside of the fragments 

 of cuticle, their swollen bases being embedded in the ectoderm. 

 Bouin, silver (see too, Text-fig. 3, gl.ec 2 ). Scale 1 20 /i { 



Fig. 6. Paraffin section through the wall of a palpon (top) with a 



portion of a villus cut transversely (bottom). Zenker, P.A.S. 



Scale 1 5°^ I 



Fig. 7. Surface view of expanded buccal endoderm from a feeding 



gastrozooid, showing rows of short cilia, and a bunch of long ones. 



Formaldehyde-sublimate, silver. Scale 1 iitfi 1 



