44 SUMMAEY OF CURRENT RESEARCHES RELATING TO 



grooves must be looked upon as the homologues of tlie liver of more 

 perfect Ascidians. The chylific ventricle is an ampullaeform dilatation 

 of the digestive tube, which communicates with the terminal intestine 

 by a cleft. The epithelium of the rectum is ciliated. The intestinal 

 gland is composed of a series of ramified tubes, which form a kind of 

 reticulum on the surface of the rectum ; they pass into a canal which 

 opens into the stomach between the gastric lobes, and the product of their 

 secretion aids in digestion. 



The seventh chapter is divided into two parts, the first of which deals 

 with the nervous system properly so called, and the second with the 

 hypoganglionic gland and the vibratile organ. The true nervous system 

 consists of an interoscular ganglion, a ganglionated end which goes to the 

 viscera, and of nerves. The first of these, or brain, is situated on the 

 mediodorsal line, is ovoid in form, and gives rise, anteriorly, to a pair 

 of nerves which go to the buccal siphon, then to two or three pairs of 

 lateral nerves, and lastly, to a large posterior nerve which runs for some 

 distance above the ganglionated cord, and which innervates the cloacal 

 siphon. Histologically speaking, the brain is made up of a peripheral 

 zone, which is formed solely by uni- or bipolar ganglionic cells arranged 

 in two or three irregular concentric layers, and of a central fibrillar 

 mass in which a few nuclei are scattered. The visceral or dorsal 

 ganglionic cord arises from the posterior and inferior part of the 

 cerebral ganglion, and is continued along the mediodorsal line between 

 the epithelium of the gill and that of the cloaca, and between the rectum 

 and the oesophagus as far as the region of the stomach. It is formed of 

 ganglionic cells and some nervous fibrils ; there are never more than three 

 or four ganglionic cells visible in one transverse section. This cord is 

 surrounded by vast vascular spaces, and is accompanied along its whole 

 length by two longitudinal muscles. The nerves are altogether fibrillar, 

 and their fibres are continuous with the fibrillar substance of the brain. 

 The posterior median is single owing to the fusion along part of their 

 length of the two nerves which, in most other Ascidians, arise from the 

 posterior region of the brain. 



The hypoganglionic gland is almost as large as the brain and lies 

 beneath it ; it is provided with an excretory canal, which is connected 

 with that of the enigmatic structure which is known as the vibratile 

 organ. It is ovoid in form, and is composed of a number of cells with 

 irregular contours ; these are most regular near the periphery of the 

 gland. In its upper part there is an elongated cavity, the roof of which 

 is formed by an epithelium of cubical cells ; this epithelium is that of the 

 e:scretory canal of the gland. There are intermediate conditions between 

 this gland reduced to a single cavity, and the compound tubular gland 

 which is found in simple Ascidians. The excretory canal may be 

 divided into three distinct regions ; in the anterior part it is complete, 

 but this is very short ; in the median part it is reduced to a simple 

 groove, while in the posterior region it is at first circular, but its cells 

 are soon arranged without order, and we have at last nothing more than 

 a mass of cells lying beneath the brain, and altogether similar to the 

 ganglionic cells of the visceral cord. 



The vibratile organ forms a funnel which acts as the continuation of 

 the excretory canal, and it opens by an oval orifice on the mediodorsal 

 line of the animal, in the centre of a projecting tubercle, which extends 

 as far as the base of the large mediodorsal tentacle. Its cells carry long 



