100 



SHELL GALLEEY. 



Specimens vary in size from a few inches to upwards of four feet 

 in length, and, as the name of the genus implies,* they are brilliantly 

 phosphorescent. Sometimes they occur in innumerable multitudes, 



Fig. 20. 



>^^^ em. em at -asc 



Section througli wall of Pyrosomci, magnified, showing a single layer of 



ascidiozooids. 



br, branchial ; at, atrial orifice ; tp, process of the test ; br s, branchial sac. 



(Herdman : Tunicata, Encyclopsedia Britannica.) 



giving rise to a zone of greenish light extending for miles. Professor 

 Moseley records that during the voyage of the Ghallenger in the 

 North Atlantic a huge specimen of Pyrosoma spinosiim, four feet 

 in length, was captured. On tracing his name on its body, the word 

 came out in letters of fire. 



In Pyrosoma ehgans (exhibited), from Naples, the ascidiozooids are 

 arranged in verticils, and the mouth of the cylinder is surrounded 

 by a movable diaphragm ; the outer end of each ascidiozooid is 

 provided with a membranous spine. Six species of Pyrosoma are 

 known. Pyrosoma atlanticwn is found in the tropical Atlantic and 

 Antarctic ; P. giganteum in the Atlantic, Pacific, and Antarctic ; and 

 P. spinosum in the South Atlantic. 



Order II. — Thaliacea. 



The Thaliacea are free-swimming Tunicates, which exhibit 

 alternation of generations in their life history. There are three 

 families, Salpidce,, OdacnemidcR, and DoUoUdcB. 



Salpidce. — The Salpas are transparent barrel-shaped organisms, 



* Pyrosoma — pur, fire ; soma, body. 



