LECTURES ON EMBRYOLOGY. 



23 



approximating thus toHolothurise, and the body 

 more elongated. We have really a still higher de 

 gree of developement. 



In the general classification of these animals, I 

 showed that the tubular form is the highest, as. 

 is seen among the Holothurice ( Plates XIV and V). 



[PLATE XIV HOLOTHURIA.] 



( Jf LA IK V iiuLOTH U K 1 A. J 



I might have shown these animals to remind you 

 of what are the species on these shores. Here is 

 the common Five finger (Plate VIII, fig. A), and 

 he;e is the common Sea-urchin (Plate XQI, fig B) 

 a spherical body covered with spines, which may 

 assist us in comparing, better than simple dia- 

 grams, these animals with their embryonic states, 

 as illustrated before. 



[PL ATI? I 



Lut us \io\v also compare those embryonic 

 \vitti the fossils of different geological epochs. How 

 the young Comatula (Plate I) casts off the stem, I 

 have already mentioned ; but if we consider its 

 embryonic form, it will compare most remarkably 

 v/ith the fossils figured here (Plate XV). In other 

 instances, however, the fossil Crinoids do not even 

 resemble the young of those of our present epoch, 

 but belong altogether to peculiar types, as figured 

 here (Plate XVII). 



I have been able to bring here a natural speci 

 men of one of these lily-like animals, in a most 



[PLATE XVII FOSSIL CRINOIDS. | 



OL OLC'.LC ur preservation, resting iu>uu it.-, h,< m, 

 which is composed of innumerable plates articu- 

 lating together. It is a Tentacriuus, from Wurt- 

 emberg, in Germany. The principal portion of the 

 animal, which is called its crown, divides into five 

 distinct rays, which are flattened down upon the 

 slab of stone upon which it rests, but so well pre- 

 served that every one of the ramifications can be 

 distingushed, and the connexion of these branches 

 upon the crown below are very distinct. (The 

 Prof, here showed a most splendid fossil, which ex- 

 cited great interest among the audience. Those in- 

 terested in this branch of natural history will find 

 the subject carefully investigated in Agassiz and 

 Gould's Principles of Zoology.) I doubt whether 

 there is another specimen so perfect as this, and I 

 would invite you after the lecture to pass by it and 

 observe it. 



The number of joints which allow the animal to 

 move and expand is enormous. One hundred and 

 fifty thousand have been computed in one of them 

 by Dr. Buckland ; in others, the number of joints 

 are fewer (Plate XV.), the crown remaining more 

 closed and the rays not dividing so extensively 



