98 MARGARET 0. COLLOUTT. 



EXPLANATION OF PLATE 1, 



Illustrating Margaret C. Collcutt's paper " Ou the Structure 

 of Hydractinia echinata/' 



(Several different colonies were examined, hence there is a slight variation in 



the size of cells, &c., figured.) 



LIST OF KEPEKENCE LETTERS. 



up.ed. Upper ectoderm. Led. Lower ectoderm, end. Endoderm. mes. 

 Mesogloea. i. c. Interstitial cell. n. Nematocyst. 71. c. Nematocyst cell. 

 gl. Gland-cell. pip. Polyp, spn. Spinule. p. m. Perisarc membrane, c. t. 

 Coenosarc tube. p.t. Perisarc tube. e. Egg-cell. f.m. Food material. 

 mo. Mouth, sk. Skeleton, v. Vacuole, m.t. Muscle tail. mes. p. Meso- 

 gloea process, d. c. Degenerating ccenosarc. nu. Nucleus. 



Fig. 1.— Series of vertical sections illustrating the transition from the 

 growing edge to the older parts of the colony, a. Section at extreme edge, 

 showing to the left a coenosarc tube surrounded with perisarc, and towards 

 the right tubes which have anastomosed. b. Section of somewhat older 

 part of the colony, where the perisarc membrane tapers off and disappears. 

 c. Section of old part of colony passing through portion of the wall of a 

 polyp, and showing the communication between the polyp and an endodermal 

 tube of the basal coenosarc. The section also shows the tabulated growth of 

 the chitinous skeleton. D. 3 cam. 



Fig. 2. — Vertical section of base of colony, showing the degeneration of 

 coenosarc and a degenerating mass isolated in a chitinous lacuna. D. 3 cam. 



Fig. 3. — Diagrammatic section of a smooth spine at the colony edge. 

 A. 3 cam. 



Fig. 4. — Optical horizontal section of two anastomosing tubes, showing 

 both commencing anastomosis and complete anastomosis. The left-hand tube 

 has given off a branch. D. 3 cam. 



Fig. 5. — Vertical section through a growing chambered spine illustrating 

 the relations of the basal coenosarc to the skeleton, and showing a chamber of 

 the spine containing coenosarc, D. 3 cam. 



Fig. 6. — Longitudinal section of upper part of blastostyle ; on the right- 

 hand side is an egg-cell, e', in the ectoderm, and two egg-cells in the endo- 



