REPORT ON THE TUNICATA. 



41 



in those forms the reproductive organs become fully developed, thus completing the 

 life-history, which may be represented diagrammatically thus : — 



Vrrcr 



Tailed larva. 



I 



Nurse 



(Blastozooid). 



I 

 Buds. 



- 1st generation. 



Nutritive forms 

 (Gastrozooid.) 



Reproductive forms 

 (Gonozooid). 



Foster forms 

 (Pliorozooid). 



2nd generation. 



The structure of the reproductive form (Gonozooid) of the sexual generation is 

 shown in the accompanying woodcut. 



Fig. 6.— Diagram of the Gonozooid of Doliolum, from the left side. 



at. atrial aperture; ai.l. atrial lobes; at.m, membrane lining pei'ibranchial cavity; by. branchial aperture; brj. 

 branchial lobes; hr.s. branchial sac; d.t. dorsal tubercle; emi. endostyle ; h. heart; i. intestine; 711. mantle: 

 m^ — 7/1^, muscle bands ; n. nerve ; ii.g. nerve ganglion ; or. ovary ; p.br. peribranchial cavity ; p.p. peripharyngeal 

 band; s.o. sense organs; i. test; s.^/. subneural gland; s(. stomach; Sf/. stigmata ; (fs. testis; r. zona prffibranchialis. 



The body is of a regular Imrrel-shape, and has wide-open branchial and atrial aper- 

 tures at its extremities. These are surrounded by lobes. The test is a very delicate 

 cuticular layer covering the surface of the squamous ectoderm. The mantle has a well- 

 developed musculature in the form of eight muscle bands (Fig. G, Hi' to rii') surrounding 

 the body. The first and eighth of these act as branchial and atrial sphincters, while all 

 the hoop-like muscles combine in causing a current of water to How through the 

 branchial and peribranchial cavities in such a way as to propel the body through 

 the water. 



The branchial sac is wide anteriorly, where it is separated from the combined 



(ZOOL. CHALL. EXP. — PART LXXVI. — 1888.) 



Grcraa fi 



