OCCURRENCE 



69 



Tiy.jP 



U.e. 



tail- 



3 cm. — it is of a bright red colour. (4) Fritillaria, Q. and G., in 

 which the body is elongated (Fig. 32) and composed of anterior 

 and posterior regions, the tail relatively short, the endostyle 



Fig. 31. — Transverse 

 section of body and 

 tail of Oikojileura 

 flahellum (?) at, 

 Atrial tube ; hl.s, 

 blood - space ; br,s, 

 cavity of pliarynx 

 or branchial sac ; 

 ec, ectoderm ; en, 

 endoderm ; ep.p, 

 epipharyngeal cili- 

 ated bands ; gel, 

 gelatinous layer be- 

 tween ectoderm and 

 endoderm ; hy.p, 

 hypo pharyngeal 

 ciliated band ; tnus, 

 muscular tissue on 

 inner surface of 

 ectoderm of tail ; 

 n, nerve-cord ; n', 

 its continuation in 

 the tail ; n.ch, noto- 

 chord in tail ; r, 

 rectum ; sg, one of 

 the stigmata or cili- 

 ated openings from 

 the branchial sac to 

 the atrial tube ; t, 



test ( = young ''house"); ,r, bridge of gelatinous tissue in front of stigma closing 



branchial sac off from atrial tube. (After Herdman. ) 



recurved, the stigmata opening far in front of the anus, and an 

 ectodermal hood is formed over the front of the body. 



In all nearly forty species of Larvacea are known. 



Occurrence. — Although for the most part transparent, and 

 usually almost invisible in sea-water, some Appendicularians may 

 have certain parts of the body (alimentary canal, endostyle, 

 gonads, etc.) brilliantly pigmented (orange, violet, etc.), and may 

 under exceptional circumstances be present in such profusion as 

 to colour tracts of the sea. Appendicularians are widely dis- 

 tributed, having been found in all seas from the Arctic to the 

 Antarctic, both round coasts and in the open ocean. Although a 

 few species have been found at considerable depths in the 

 Mediterranean, still in the Atlantic they are not deep - water 

 animals, and as a group must be regarded as surface-forms. 

 They are fairly abundant to a depth of 100 fathoms, and some 

 few reach 1500. Species of Oikopleura and Fritillaria are 



71.0%. ^^' 



