ON THE EMBRYOLOGY OF ECIIIXODEKMS. 



23 



place in Starfishes, Echinoids, and Ophiurans, as well as Holothurians, and thus the 

 distinction drawn by Midler falls to the ground. I lie young of Cuvicria figured here 

 resemble the figures of Miillcr on Plate IV. third Memoir,* and Plate VII. fourth 

 Memoir.f The young Holothurians (figs. 35 - 38) can without doubt be referred to 

 Cuvieria on account of their color ; they are of a brilliant vermilion. This unfortu- 

 nately renders them so opaque that we cannot trace the position of the different 



organs without strong compression. In the youngest Cuvicria observed (fig. 35), 



the pupa (I) is very large; the Holothurian has not rcsorbed it to any extent; 

 the tentacles (g) cannot be protruded. In a somewhat more advanced specimen 

 (fig. 36), the Holothurian seems to have resorbed a considerable portion of the pupa 

 (I) ; the tentacles (g) protrude ; they are simple, do not branch, and terminate with 

 knobs. The only tentacles present are those round the mouth. In a still more 

 advanced stage (fig. 3T), the tentacles show the first tendency to forking (g)\ other 

 tentacles, ambulacral tentacles (/), are also developed. The madreporic body stands 

 out at the extremity of a small tentacle, b. That this is truly the madreporic body 

 can easily be seen by compressing specimens of the age of fig. 36, when the madre- 

 poric body will be seen at the extremity of a tube, connecting thus the outer medium 

 with the water-tubes in exactly the same manner as in Starfishes, Echinoids, and 

 Ophiurans. The presence, also, of a calcareous network, is the best proof of its 

 future function. During resorption this canal becomes liberated, but shrinks soon 

 so as to bring the madreporic body on a level with the general outline. 



On compressing a young Holothurian, about in the state of fig. 37, we shall obtain 

 an idea of the state of development of the different parts. Fig. 38 (a Holothurian 

 thus compressed) shows the separation of the main cavity into a kind of oesophagus, 

 a stomach, d; and an intestine, c, with the anus, a. In younger specimens, when 

 compressed, there is no anus, and the stomach is a simple sac without the peculiar 

 bent addition of the intestine, c, of fig. 38. There are likewise no Y-shaped rods 

 deposited on the surface of the body, and the ring of limestone particles at the base 

 of the tentacles is not as fully developed as in this figure. (Fig. 38.) The madre- 

 poric body is seen more clearly in younger stages to connect with a large sac, w\ 

 which is probably the remnant of one of the water-tubes, from its connection with 

 the tube leading to b. Although externally (fig. 37) we see but two ambulacral 

 tentacles, yet on compressing this specimen we should find that there were others 

 already formed, but in such a rudimentary state that they do not as yet force their 



Muller, J. Ueber die Larven und die Metamorphose der Holothurien und Asterien. Berlin, 1850. 

 t Muller, J. Ueber die Larven und die Metamorphose der Echinodermen. Berlin, 1852. 



