Literary Notices. xxxi 



tinal ganglia on the other hand, are formed on either side of the mid- 

 body region, but, by reason of the torsional growth, one comes to lie 

 above, the other beneath the intestine. The visceral ganglion springs 

 from the ectoderm of the mantle cavity. 



Histological Studies i.n the Nervous System of Leeches. i 



Dr. Rhode comes to the somewhat startling conclusion that "con- 

 trary to the generally accepted doctrines and my own earlier views, all 

 fibrous elements within the nerves, commissures and ganglia, and even the 

 ganglion cells themselves are composed of non-nervous co'nnective tissue, 

 while the real nervous substance is a homogeneous material filling the 

 interspaces between the fibrillas. Fontobdella is most minutely described. 

 Unfortunately the methods by which the very remarkable results are 

 attained are not given and we are only left to infer from indications 

 that alcoholic carmine played an important role. 



Nervous System of Nematoda. 



Hamann states- that two sorts of ganglion cells exist in all the species 

 examined (in contrast to Echinorhynchidae, where only the giant cells are 

 present). In the anal ganglion the large cells have a symmetrical uniform 

 arrangement. The skin papillae are typical sensory organs. A nerve can 

 be followed into them where it expands into a large ganglion cell of com- 

 plicated structure. 



The Development of the Nervous' System of the Holothur- 



OIDEA.-^ 



At the eighth stage of development the annular and radial parts of 

 the nervous system both consist exclusively of closely compacted cells in 

 several layers. In a latter stage fine fibres appear beneath the cells 

 parallel to ring-nerve, and after the 13th day irregularly scattered cells 

 between the fibres. As early as the 8th day the median ventral nerve 

 Anlag reaches beyond that of first pair of feet. Histologically the radial 

 nerves, like the annular, consist of a superficial cell-layer and a deeper 

 fibre tract which is seggregated distad, but in the latest stages examined 



1. Rhode, Emil. Histologische Unter.suchungen neber das Nervensystem der 

 Hirudineen. Matur. u. Nat. Mittheil. Preus. Akad. Berlin. Jan. 1891, I, p. 11. 



2. Mittheil. Berlin Akad. Jan. 1891, p. 48. 



3. Lldwig, Herbert. Zur Entwickelun.sgeschicte der Holothurien. Mat. u. 

 Naturw. Mittheilungeu Kong. Preus. Akad. Berlin, Feb. 1891,2, p. 85. 



