276 Miscellaneous. 



On the Histological Constitution of certain Nematodes of the Genus 

 Ascaris. By M. L£on Jammes, 



Naturalists who have studied the histology of the Nematodes 

 up to the preseut time have asserted that the layer named by them 

 granular lager was not cellular in the adult. Leuckart, however, 

 thought that there existed an epithelial layer formed by very small 

 elements, situated internal to and close against the muscle-cells. 



In the investigations in which I am engaged, on certain species 

 of Nematodes, and in particular Ascaris megalocephala, A. Inmhri- 

 coides (calf), and A. suilla (Dnjardin), I have never been able to 

 establish the existence of this layer. With the aid of the histo- 

 logical apparatus in use at the Faculty of Sciences of Toulouse I 

 have long sought in the granular layer for any traces of an ectoderm. 

 The granular layer is limited on one side by the cuticle, on the 

 other by t?ie muscular layer. 



But, on the other hand, these researches have brought to light 

 certain particulars relating to the granular layer : transverse sec- 

 tions at the horizon of the oesophagus show the continuity and 

 structural identity of the oesophageal nervous ring and of the 

 granular layer. Both are made up of fibrils interspersed with cells. 

 The fibrils of the nervous ring on arriving at the body-wall bend 

 inwards and distribute themselves between the cuticle and the 

 muscular layer; after this the nervous system and the muscular 

 layer affect connexions so fine that it is impossible to assign their 

 exact limits. 



Longitudinal sections at different horizons show little beds of 

 cells in the granular layer, often disposed in several rows but never 

 forming a continuous epithelium. 



These cells present various appearances : rarely cubic, sometimes 

 rounded, most often flattened parallel to the body-wall, they bear a 

 variable number of prolongations. It is these prolongations which 

 contribute to give the layer its fibrillar and felted aspect in the 

 sections. 



No intercellular substance is ever found between them. 



The cells of the granular layer are stained a uniform violet by 

 chloride of gold, whilst this reagent colours the cuticle rose and 

 purple. The external segmentation as revealed bjf this infiltra- 

 tion does not correspond, at least in the adult, with any internal 

 metamerization. 



The great similitude of structure of the granular layer and of the 

 nervous system leads us to think that the granular layer represents 

 the ectoderm. This latter would differ much in its constitution 

 from the ectoderm of other Metazoa ; it would be made up, in effect, 

 of neuro-epithelial elements, and the nervous system described by 

 authors would only be a condensation of this mass at difterent points 

 in the body. 



However, this idea needs corroborating by embryological re- 

 searches, in which I am now engaged.- — Comjjtes Bendus, July 7, 

 1890, p. 65. 



