153 



EXPLANATION OF PLATE XIV. 



Fig. 1. A portion of the new membranous lip of Helix aspersa, in its natural state, 

 with cytoblasts and cells in progress of development. 

 a, a, a. Vascular tissue in progress of formation. 



Fig. 2. A portion of the lip of the same shell. 



a, a, a. Vascular tissue in its early stage of development. 



Fig. 3. Detached cells and cytoblasts in various stages of development, from the young 

 lip of Helix aspersa. 



Fig. 4. Linear arrangement of nucleated cells, illustrating the early stage of the de- 

 velopment of prismatic cellular tissue, in the young lip of Helix aspersa. 



Fig. 5. Interstitial vascular tissue of Ostrea edulis, separated by maceration in dilute 

 hydrochloric acid. 



Fig. 6. Interstitial vessels running in the angles of the terminations of the cells at the 

 inner surface of Pinna. 



a, a. The vessels in situ. 



b, b. The impression left by the vessels after they have been removed. 

 Fig. 7. Interstitial vessels similar to those represented in fig. 6, but partially hidden 



by the gelatinous looking covering. 



a, a. The vessels exhibited by the absence of the covering. 



b, b. Portions of the preparation where the vessels are concealed by the 

 covering. 



Fig. 8. Section of prismatic cells of Pinna ingens, at right angles to their axes, show- 

 ing the layers of vessels connected by the membranous tissue of the sides of 

 the cells. 



EXPLANATION OF PLATE XV. 



Fig 1. Cyprcea Mauritiana fractured at right angles to the lines of growth. 



a, a. Part of the central stratum of plates of prismatic cellular structure, 

 crossing each other at right angles. 



b. The outer stratum of plates of prismatic cellular structure, exhibiting 

 the basaltiform columnar appearance arising from the section being at 

 right angles to the planes of the plates. 



Fig. 2. Prismatic cellular structure of the thin stratum from the interior of a Conns, 

 showing the mode in which the cells frequently divide or unite with each 

 other. 



Fig. 3. Upper surface of periostracum of Trigonia Lamarckii, with its cytoblasts. 



Fig. 4. One of the cytoblasts magnified 1020 linear. 



EXPLANATION OF PLATE XVI. 



Fig. 1. Cellular structure of Haliotis rubra. 



a, a, a, a. Sections of Haversian canals. 

 Fig. 2. A portion of a plate of fan-shaped prismatic cellular tissue from a bivalved 

 shell from the gault formation. 



a, a, a, a. Longitudinal Haversian canals. 



b, b, b, b. Transverse Haversian canals. 



M 2 



