20 



ZOOLOGY 



SECT. 



n.gl.) which has sometimes been correlated with the hypophysis 

 of the Craniata. A duct (Fig. 729, dct., and Fig. 730, gld) runs 

 forward from it and opens into the cavity of the pharynx ; the 

 termination of the duct is dilated to form the ciliated funnel, and 

 this is folded on itself to form a prominence, the dorsal tubercle, 

 which projects into the cavity of the pharynx. The dorsal tubercle 

 may be a sensory organ : the neural gland may have to do with 

 excretion. 



The excretory system seems to be mainly represented by a 

 single mass of clear vesicles, without a duct, lying in the second 

 loop of the intestine. In the interior of these are found concretions 

 containing uric acid. 



Reproductive System. The sexes are united. The ovary 

 and the testis are situated close together on the left-hand 



n.gl- 



Fia. 730. Antero-dorsal part of Ascidia, showing the relations of the layers of the body and 

 of the nervous system, A, in sagittal section ; B, in transverse section, d. bl. s. dorsal blood- 

 sinus ; d. 1. dorsal lamina ; d. n. dorsal nerve ; d. t. dorsal tubercle ; ect. ectoderm ; en. 

 endoderm ; e. p. br. epithelium of peribranchial cavity ; gl. d. duct of neural gland ; /. v. 

 points to the ciliated epithelium covering a longitudinal vessel of branchial sac (pharynx) ; 

 m. mantle ; n. nerve ; n. g. ganglion ; n. gl. neural gland ; p. br. peribranchial cavity ; pp. b. 

 peripharyngeal bands ; sph. oral sphincter ; t. t t'. test ; in. tentacle. (After Herdman.) 



side of the body in the intestinal loop. Each of them contains 

 a cavity which, like the pericardium and the cavities of the 

 excretory vesicles, forms a part of the original coelome. Con- 

 tinuous with the cavity of each is a duct oviduct or sperm-duct, 

 as the case may be which opens into the atrial cavity close to 

 the anus. 



The development of the Ascidian is described below (p. 30). 



2. DISTINCTIVE CHARACTERS AND CLASSIFICATION. 



The Urochorda are Chordata in which the notochord is confined 

 to the tail region, and, in all but the Larvacea, is found only in 



