86 



ASCIDIANS 



od 



this genus there may be dimorphism in the buds, some of them 



placed deeply in the stalk 

 having a large amount of 

 reserve food-matter in their 

 ectoderm, and remaining 

 dormant until required to 

 regenerate the " head " or 

 upper part of the colony 

 when it is lost. This genus 

 was made known by the 

 " Challenger " expedition. 

 The species are mostly trop- 

 ical, or from southern seas. 

 Fam. 2. Coelocormidae. 

 -Colony not fixed, having 

 a large axial cavity with 

 a terminal aperture. Bran- 

 chial apertures five-lobed. 

 This includes one species, Coelocormus huxleyi, Herdman, which is 

 in some respects a transition-form between the ordinary Com- 

 pound Ascidians {e.g. Distomatidae) and the Ascidiae Luoiae 

 {Pyrosoma, see p. 90). 



«mts 





epc 



p:c. 



Fig. 48, 



■Transverse section of the abdomen of a 

 Distomid. hl.s, Blood -sinus ; ec, ectoderm ; 

 cp.Cy epicardiuni ; gl^ intestinal glands ; A, heart ; 

 i, intestine ; /. m, longitudinal muscles ; ')nes, 

 mesoderm ; o.d, oviduct ; p.c, pericardium ; st, 

 stomach ; v.cl, vas deferens. (After Seeliger. ^ 



br S. 



vd. 



-v.d 



Fig. 49. — Section oi-Leptodinum colony, showing the distribution of spicules and parts 

 of the ascidiozooids. b, Base of colony ; hr, branchial aperture ; br.s, branchial sac ; 

 sp, spicules ; st, stomach ; tes, testis ; v.d, vas deferens. 



Fam. 3. Didemnidae.- — Colony usually thin and incrustino-. 

 Test containing. stellate calcareous spicules (Figs. 49 and 50, B). 



