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form bands. Sexual and asexual reproduction. Life- 

 history shows alternation of generations (metagenesis). 



Examples, Salpa. Body barrel -shaped, with mouth at one end 

 and atrial opening at or near opposite end. Test 

 thin and transparent. Muscles like incomplete 

 hoops. Pharynx simple, with two large holes 

 instead of gill-slits. Without a tailed larva. 

 Embryo (nourished by a " placenta ") becomes a 

 solitary asexual form, which, by budding, pro- 

 duces a chain of sexual zooids, which produce 

 the asexual forms (metagenesis). 

 Doliolum. Body barrel-shaped, with mouth at one 

 end and atrial opening at opposite end. Test 

 thin and transparent. Muscles form complete 

 hoops. Pharynx simple, with few gill-slits. 

 The tailed larva develops into an asexual (" nurse") 

 form, whioh, by budding, produces three different 

 kinds of buds (polymorphism), namely, nutritive 

 buds (which feed the " nurse ") and " foster- 

 mothers," to which are attached for a time those 

 buds which become sexual forms. 



Order LARVACEA or APPENDICULARIAE. Solitary and pelagic 

 Ascidians of. minute size, with long tails and notochord 

 present throughout life. Form very large tests (tempor- 

 ary " house ") within which they move about freely and 

 which they often vacate. After remaining " houseless " 

 for a time, the Appendicularian forms a new test within 

 a few hours. Mouth anterior. Anus ventral, at root of 

 tail. . Gill-slits (two) and anus open directly to outside 

 (without an atrium). Dorsal nerve cord, extending into 

 tail, with cerebral ganglion and otocyst and from 8 to 

 40 caudal ganglia. Hermaphrodite (protandrous), 

 except Oikopleura. 



Examples, Appendicularia. 



Oikopleura. Tail very long. Not hermaphrodite, 



SUB-PHYLUM CEPHALOCHORDA. 

 Amphioxus or Branchiostoma (The Lancelet). 



Describe the External Features of Amphioxus. Where is 

 it found ? 



Amphioxus is small (about 2 inches in length) and fishr 

 like ; its body, almost colourless and translucent, is elongate, 

 compressed at the sides, and pointed at the ends. Each 

 side is marked by a close succession of <^ shaped line$, 

 which indicate the connective tissue septa between the 

 <^ shaped myotomes or segments (62) of ithe lateral 



