149 



mode of disposition is so familiar to every observer of the blood by 

 means of the microscope. 



It is difficult to divine to what extent this law may obtain under 

 other circumstances, but we have every indication of its operating ex- 

 tensively in numerous cases of the origin and increase of newly-formed 

 animal tissues in the Corallidai and the Spongiadce, as well as in the 

 beautiful and highly organized subjects of the present paper, in the 

 membranes of which we have seen it exerted in the mutual attraction 

 and arrangement of the cytoblasts for the production of the new vas- 

 cular tissues of the periostracum and other tissues of the shell. The 

 same law also appears to be called into action in the production of the 

 muscles of animals ; for Bowman, in his paper on muscular fibre, pub- 

 lished in the ' Philosophical Transactions ' for 1841, says at p. 484 : 

 "It is now well known through the researches of Valentin and Schwan, 

 that the fasciculi of voluntary muscle in the earliest stage of their de- 

 velopment, consists of a series of nucleated cells, and that the nuclei 

 continue visible during the period of foetal growth." 



There is another phenomenon which accompanies the restoration 

 of the wounded parts of the periostracum of the shell, which is ex- 

 ceedingly interesting, as it appears to be the result of a natural effort 

 in aid of the reproductive process; very nearly allied to that which is 

 attained by Nature in the healthy marginal inflammation of the 

 wounded parts in the fleshy tissues of the warm-blooded animals. 



If we examine the outer margin of the wounded spot in the perios- 

 tracum, with a power of 200 or 300 linear, we always observe that 

 it presents a finely-fringed appearance, like dendritical filaments, 

 springing from the extreme margin of the healthy periostracum, and 

 penetrating its substance to a small extent, as represented at PI. xvii. 

 fig. 8. If we examine this object with a power of about 1000 linear, 

 we find that this appearance is caused by the healthy periostracum 

 immediately surrounding the wound being excavated into an infinite 

 number of short bifurcating canals, of nearly equal diameters, as re- 

 presented at a a, fig. 1, PI. xviii. There is to all appearance but one 

 thin stratum of these curious organs, and this by measure is r0 ^ o - inch, 

 beneath the outer surface of the periostracum. I have been unable 

 to detect them in the space between this layer and the basement mem- 

 brane. In some cases they extend much further beyond the dark 

 margin of the new tissues than is represented in fig. 1, PI. xviii.; and 

 in one instance I found a circular patch of them radiating from a 

 small dark dot near the centre of the patch, as if the reparative pro- 

 cess had been completed, and they alone remained as an evidence of 



