Marvels of the Universe 



569 



Many new species of Sea-pens were discovered during the Challenger expedition of 1873-76. 

 Amongst these was the beautiful Tentacled Sea-pen shown on page 566. It was dredged up from 

 a depth of ten to twelve fathoms off the coast of the Phihppine Islands. Each frond or pinna, 

 which spread out fan-shaped from the main stalk, is fringed with delicate, white, tentacled polyp-cells 

 — Whence its name. These cells, and the polyps themselves, are so minute that they can only just be 

 detected in the illustration. The main stem and the bases of the branches are of a reddish hue. 

 But perhaps the most splendid of all is Thomson's Sea-pen, named after the leader of the Challenger 

 expedition, which was found at the immense depth of six hundred fathoms off the coast of Buenos 

 A\T:es. Its average length was about four feet. The thick swelling stalk with a smaller end bulb 

 has a pointed free end which is buried to a considerable depth in the rnud. The rather fleshy main 

 stalk does not branch out into well-defined pinnules or fronds, edged with polyp cells, as do those 

 on page 565, but the polyps themselves are ranged in a curved line round the stalk, and are thickly 

 placed, eight or ten forming a single curved fringe. The polyps are entirely separate from one another 

 even in their growth from the stem. They are very long, and the cells which are usually noticed 

 and which form a distinctive feature of the Tentacled Sea-pen are absent. The polyps in this 

 instance, however, are supplied with long tentacles which are seldom withdrawn, and careful observa- 

 tion has ascertained that these tentacles are themselves supplied with long threads or pinnules. Of 

 the species found round the British coast perhaps the most interesting is the Wonderful Sea-pen. 

 It is common in the waters to the East and North of Scotland and is to be found off the coast of 

 Xonvay ; but the extremely fragile structure of this Sea-pen makes a perfect specimen a rarity. 

 It is one of the finest of marine polyp-systems. There are two series of half moon shaped 

 wings which are wrapped round the main stem and spread out after the fashion of branches. 

 These series have the appearance of two ornamental ribbons folded in an inverse direction 

 round the stem and develop ornamental wings alternately. These wings are waving, vandyked 



Pfiolo 61/] 



[y. E. Cooper. 



THE PERIWINKLE'S HOOKED TEETH. 



They act as sickles to scrape off minute seaweeds for food. 



