42 THE VOYAGE OF H.M.S. CHxU,LENGER. 



branchial sipliou and prebrancliial zone (there are no tentacles to form the usual 

 boundary between those two regions) by the peripharyngeal bands, and tapers slightly 

 to the rounded posterior end, which is placed between the fifth and sixth muscle bands. 

 The stigmata are arranged in two series on each side of the sac. The dorsal series 

 commences at tli^ third muscle band and extends posteriorly to the end of the sac ; 

 while the ventral series runs from the fourth band anteriorly to beyond the fifth 

 posteriorly, where it joins the corresponding series of the other side. 



The endostyle is straight. It extends from between the second and third to 

 between the fourth and fifth muscle bauds (Fig. G, end.). There are no dorsal languets. 



The nervous system consists of a single ganglion placed in the mantle in the mid- 

 dorsal line between the third and fourth muscle bands. It gives off distributory nerves 

 anteriorly and posteriorly. The sense organs consist of some groups of modified 

 epithelial cells in which nerves end, placed upon the branchial and atrial lobes. In the 

 Blastozooid, however, there is in addition an otocyst placed on the left side of the 

 body between the third and fourth muscle bands, and the ganglion lies l^etween the 

 fourth and fifth muscle bands. 



On the ventral surface of the ganglion is found the usual subneural gland, with a 

 delicate duct which runs forward to open into the prebranchial zone in the mid-dorsal 

 line by means of a funnel-shaped cavity richly ciliated internally (Fig. 6, d.t). The 

 rounded opening of this ciliated funnel is surrounded by the spirally-coiled dorsal ends 

 of the peripharyngeal bands. 



The peribranchial cavit)^ is a large space lying posteriorly to the branchial sac, 

 and opening externally by the terminal atrial aperture. It has an anterior lateral 

 extension on each side of the branchial sac into which the stigmata open. 



The alimentary canal is curved so as to form a V'^'^li'^P^d loop, concave dorsally, 

 placed at the posterior end of the branchial sac, and occupying the ventral part of the 

 peribranchial cavity. The cesophagus is a short wide tulje running backwards to open 

 into the rounded stomach. The intestine springs from the posterior end of the 

 stomach, and rims at first posteriorly and then dorsally to open into the peribranchial 

 cavity near its middle. A system of digestive tiibules ramifies over the greater part of 

 the wall of the intestine, and opens by a duct into the stomach. 



The heart is placed ventrally, close to the oesophageal aperture. The hermaphrodite 

 reproductive organs lie ventrally, and open into the peribranchial cavity close to the 

 anus. The ovary is a small rounded sac, but the testis is a greatly elongated tube (see 

 Fig. 6, tes.), which varies in its extent and shape in difi"erent individuals of the same 

 species.' When fully developed it may extend anteriorly as far as the first muscle 

 band. It lies at the left side of the body. 



In Uljanin's recent monograph on the genus Doliolum only four species are 

 recognised : — 



' Sec Trans. Botj. Soc. Ediii., vol. xxxii. part i. pi. xx. figs, (i-ll, 1S83. 



