162. On Cyrtoma, a new genus of Fossil hli'iuidu- 



decay, and that is subject to the same laws as the absorbents 

 in other beings. A vertical fissure is observed to form over 

 the situation of the suture, by which each pair of anambulac- 

 ral plates are joined together in species that have attained 

 a certain size, and this would seem to deepen with the 

 advancement of age, and finally the globe or shell separates 

 into five equal parts, the sections taking place from api- 

 ces of the five oviducal plates which surround the anus, and 

 descend from thence over the disc to the mouth. Thus the 

 complicated and beautiful skeleton consisting of 540 pieces 

 in the young animal, adjusted with mathematical precision, 

 are gradually consolidated in the adult, and as life advances 

 towards the close, the shell separates into five pieces, each 

 equivalent to 108 elementary plates, but which are at this 

 stage so firmly united, that if sufficient force be applied 

 the parts fracture through the middle of the former plates, 

 rather than separate at their respective junctions. 



It is necessary now to compare these observations with 

 the views generally received on the subject up to this time. 

 Professor Grant has the merit of being the first comparative 

 anatomist in Great Britain, whose works afford any thing 

 like a complete view of what is known of the general struc- 

 ture of the animal kingdom, and has still the far higher 

 merit of having himself contributed materially to our know- 

 ledge of the structure of animals both by his lectures 

 and original researches. On this subject he observes in his 

 lectures, p. 271, "In these animals," (echcini) "when we 

 observe the manner in which the skeleton is constructed, we 

 find the same component pieces which surround the body 

 of the Asterias are developed, meet each other, become con- 

 solidated by numerous layers, and thus form the great 

 globular disc." The words in italics were it not for the 

 next sentence, would convey the true state of the case ; but 

 Dr. Grant continues, " The ambulacra of the Asterias are 



