638 RECORD OF CURRENT RESEARCHES RELATING TO 



which generally conceal it. Segmentation takes place in the midst of 

 the nutritive yolk, the egg-cell not issuing from it previously, as in 

 Tcenia. As it increases in size it drives the yolk-globules to the 

 periphery, where they often present the appearance of polygonal cells. 

 After segmentation the egg consists of finely granular cells, but 

 slightly connected with each other ; it undergoes delamination in the 

 same way as in TcBnia ; the central part forms alone the six-spined 

 embryo, the external part becoming clothed with cilia, and constituting 

 the " embryophore," within which the embryo lives free. The latter 

 and its capsule emerge from the egg on the disappearance of the egg- 

 operculum, and rapidly (in one or two seconds) become far greater in 

 size than the egg itself. This is owing to the absorption by the 

 embryophore of a large quantity of liquid, converting it into a finely 

 granular and very delicate reticulum. The cilia now rotate the 

 whole ; they are short and uniformly distributed ; a slight pressure 

 expels the embryo, which after abandoning the embryoj)hore, creeps 

 about by amoeboid movement, showing its constituent cells plainly. 

 It is therefore the embryophore — and not the embryo, as stated by 

 M. Donnadieu — which moves as if it was ciliated, and the existence 

 of the cilia upon it, pointed out by Leuckart and others, is beyond 

 all doubt. 



Nervous System of the Trematoda.* — Dr. Lang's second com- 

 munication on this subject commences with an account of the nervous 

 system of the Tristomida. After reviewing the works of earlier writers, 

 among whom Blanchard, Kolliker, and Taschenberg (1879) have been 

 the most conspicuous, he proceeds to give an account of his own inves- 

 tigations on Tristomum molce. The best subjects for investigation are 

 the smaller specimens, on account of their greater transparency ; the 

 principal parts of the nervous system can be made out in the living 

 examples, for the pale nerve-cords are composed of coarse fibres, just 

 as in Planocera Graffii among the Dendrocoelous Turbellaria. 



The flattened body of these creatures has its periphery almost round ; 

 at the anterior end of the ventral surface there are two oral suckers, 

 and in their neighbourhood the margin of the body is so indented as to 

 give the appearance of a quadrangular median lobe. The abdominal 

 sucker is very large and powerful, and is connected by a short thin 

 stalk with the body. On either side of, and not far from the pharynx, 

 there are two vesicles belonging to the water- vascular system. The 

 cerebrum lies anteriorly and superiorly to the j^harynx and mouth ; 

 in form it is a short, pretty broad transverse band, with a concave 

 posterior edge. There are connected with it four small pigment spots. 

 On each side of the cerebral mass there are given off four nerves, 

 which are thus distributed. The most anterior pass to the region 

 between the oral suckers, where they branch and anastomose. The 

 succeeding nerves supply the oral stickers themselves, and have con- 

 nected with them the third pair of nerves, part of which cross over, 

 however, to the oj^posite side of the body. Where they unite in the 

 middle line, an unpaired nerve passes forwards to the cephalic lobe. 



* • Blittli. Zool. Stat. Neapel," ii. (1880) p. 28. 



