86 



ASCIDIANS 



CHAP. 



o.d/. 



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



placed deeply in the stalk 

 ec , having a large amount of 



. ll.s. 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 Luciae 

 (Pyrosoma, see p. 90). 



ep.c. 



FIG. 48. Transverse section of the abdomen of a 

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

 cp.c, epicardium ; gl, intestinal glands ; h, heart ; 

 i, intestine ; l.m, longitudinal muscles ; mes, 

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

 stomach ; v.d, vas deferens. (After Seeliger.) 



I--SP 



br.s.- 



vd.-: 



FIG. 49. Section of Leptoclinum colony, showing the distribution of spicules and parts 

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

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



Fam. 3. Didemnidae. Colony usually thin and incrusting. 

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



