568 



Marvels of the Universe 



Each barb is divided 



THE THORNS' SEA-PEN. 



nto layers, which are separated by Hard but brittle white needle 

 the rosetied polyps are protruded. 



\_Iiy Theo. Carreras. 



Between the needles, or spines. 



go to form the whole structure of the Pen, but although so numerous, thej' all act by one movement 

 and have one central axis connected with a system of obscure circulation 



As far as can be ascertained, the separate polyps play no part in the production of the ova, which 

 are formed in the cavities leading from the fleshy compartments of the extremity. These cavities 

 were found by the late Charles Darwin to be " filled with a yellow pulpy matter which under a 

 microscope consisted of round, semi-transparent grains aggregated together into particles of various 

 sizes. All such particles, as well as separate grains, possessed the power of rapid motion, generally 

 revolving round different axes, but sometimes progressive." 



Some of the Sea-pens have been observed to suddenly withdraw themselves bodily into the 

 mud when they have been slightlj/ touched. On the other hand, the lower stem, or rachis, has 

 considerable power of expansion in some species, and this part is always free from polyps. They 

 have been dredged from great depths, and they are generally found in somewhat large numbers 

 wherever discovered. This seems to show that they make but little use of the slight powers of 

 movement which they are said to possess. 



The name " Cock's-comb " is sometimes applied to the Sea-pen, and, seen in the right position, 

 with a colour which does actually resemble the decoration on the head of a domestic fowl, the name 

 is somewhat appropriate. 



We have seen that in the sponges and corals those minute pieces of mineral known as spicules are 

 invariably found. So in the flesh of the Sea-pens similar spicules are found, and these tend no doubt 

 to give some slight support to the jelly-like flesh. We seem to see here the commencement of that 

 solidification of the integument which afterwards enclosed the flesh inside a hard skeleton in the case 

 of the crustaceans and the sea-urchins. 



The straight internal rod or axis is longest in the genus of the Sea-Pens known as the virgu- 

 laria, and one of the rods in the Natural History Museum measures no less than three feet long. 

 The fossil rods of similar creatures have been met with in the London Clay of Sheppe}', but they are 

 extremely rare. 



