INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 453 



intimately connected in character witli the sensory cells. The authors 

 are of opinion that this indicates that the ganglion cells were primi- 

 tively situated in the epithelial layer, and only graduall)' passed from 

 being sensory cells to their later function and position. Successful 

 preparations demonstrate that the nervous layer is connected with these 

 sensory cells. As to the distrihution of the ganglion cells, it is shown 

 that the largest and most numerous are found arranged in several 

 circles at the base of the tentacles, and in the intermediate tissue ; 

 thence pass off bands of cells slightly separated from one another, 

 which converge radially towards the mouth, becoming rarer as they 

 get nearer to it. In the tentacles the fibrillag may be seen to have 

 mostly a direction parallel to their axis, while the ganglia are smaller 

 and are far less common than in the disk. 



The muscular layer consists of long, very thin, and smooth fibres, 

 plosely applied to one another ; in the centre of each there is a small col- 

 lection of protojilasmic matter which surrounds the nucleus (Schwalbe); 

 the longitudinal muscles of the tentacles pass at their base into tlie 

 muscles of the oral disk ; these take a radial direction. 



Mesoderm : this is the musculature of Milne-Edwards and the 

 earlier writers. In the tentacles it forms a very thin and easily pre- 

 pared layer ; it is seen, when separated, to have the same thickness in 

 all regions, and to be made up of fibres connected together by a 

 homogeneous intermediate substance ; connective-tissue cells, stellate 

 or spindle-shaped, are found in considerable numbers among the fibres. 

 Careful focussing will sometimes reveal the presence of an outer 

 layer in which the fibrillar are set parallel to the long axis of the 

 tentacles, and of an inner layer in which the constituent parts run at 

 right angles to these. In the oral disk the mesoderm is increased in 

 quantity, and the fibrilla) interlace very closely with one another. 

 The authors direct attention to the higher degree of complexity 

 attained to by the mesoderm of Tealia, in which fibres, primarily 

 ectodermal in origin, enter into the composition of the mesoderm. 



Endoderm : when this layer is examined in a longitudinal section of 

 a tentacle, it is seen to consist of a muscular layer and of a sinijile layer 

 of cylindrical epithelial cells ; the latter are distinguished from those 

 of the ectoderm by the length and singleness of their ciliary processes ; 

 in addition to those elements there arc two others which are partly of a 

 nervous and jiartly of a glandular character ; and further there are 

 special bodies wliich, in the ojjinion of the authors, are parasitic 

 organisms ; these they denominate tlie yellow cells ; found in AnOwa 

 cereus, A. cinerea, and Adamsia diaphana, they are rounded bodies 

 with a diameter of from 7-10 /x ; tlicy are surrounded by a doubly con- 

 toured membrane, and are easily isolated ; their contents consists of 

 more or less yellowish granules provided with a nucleus ; they are 

 the cause in many cases of the peculiar coloration of the animal. 



In supi)ort of their view tliat these yellow bodies are parasitic ia 

 origin, the authors point out thut («) The yellow cells are also found 

 in the mucus whicli is so abundantly jjoured out by the Aetinia\ 

 (6) Tliey are found from the tip of the tentacles to the disk in some 

 species, wliile in others they are never, or at least only sporadically 



