1876.] 21 [Minot. 



layers from the base of the epidermal cells. The descriptions hitherto 

 given of the epidermis of Cestods, and probably also of the Trema- 

 tods, are incorrect. The true epidermis has never yet been mentioned, 

 for it falls off very easily, leaving behind the thick basement mem- 

 brane, which has been described as the cuticula by all authors since 

 Leuckart, 1 and consequently the subepidermal layer of gland cells 

 has been wrongly held for the epidermis. The muscles form several 

 layers under the basement membrane (Hautmuskeln), and pass as 

 sagittal fibres through the parenchym in various directions. They are 

 highly developed, except in the parasitic forms, where the various 

 layers are less differentiated. There seem to be typically three layers 

 of body muscles, an external longitudinal, middle transverse and 

 interior longitudinal; but in many forms one or the other of the lay- 

 ers is apparently wanting. There are frequently suckers (Trema- 

 tods, some Cestods, and among the Dendrocoela, Eurylepta argus and 

 Mzsodiscus nov. gen.), which always consist chiefly of parallel fibres 

 perpendicular to their surface. The digestive canal has only one open- 

 ing, and is lined by a cylindrical epithelium. It is wanting in Am- 

 philina* 2 and all Cestods. When present, it is provided at its anterior 

 end either with a muscular pharynx (Trematods and some Rhabdo- 

 coela) or with a prehensile muscular proboscis (Dendrocoela and most 

 Rhabdocoela). The canal itself is either a simple tube or sack, or it 

 forks shortly behind the pharynx or proboscis. The space between 

 the digestive canal and the epidermis is filled with muscles and con- 

 nective tissue, which is formed of stellate and round cells, encloses 

 unicellular glands, and is furnished with many cavities in which the 

 remaining organs lie, and which may therefore be regarded as the 

 representatives of the body cavity. This connective tissue is called 

 the parenchym. The nervous system consists of a single anterior 

 ganglion, built up by a central meshwork of fibres, and of peripheral 

 ganglionic cells. Nerves radiate from it in various directions. It is 

 most distinct and compact in marine Planarians. It has a simpler 

 form in the Trematods, and is entirely wanting in Cestods. Schneider 

 describes a nervous system in Ligula, etc., mistaking another structure 

 for it, as I will explain presently. Eyes are not found in the parasitic 



1 R. Leuckart. Die Menschlichen Parasiten, Bd. I, p. 167. 



2 Salensky. Ueber den Bau und die Entwickelungsgeschichte der Amphilina G. 

 Wagen. (Monostomum foliaceum Rud.) Zeitschr. f. Wiss. Zool., xxiv (1874) 

 p. 291. 



3 Untersuchungen liber Platthelminthen. Giessen, 1874. 



