198 Royal Society : — 



nous portion of the integument. This layer is one of great import- 

 ance in the economy of these animals ; the author looks upon it as 

 the deep formative portion of the integument, from which the chi- 

 tinous lamellae are successively excreted. It is bounded internally 

 by a fibrous membrane, which serves as an aponeurosis for the at- 

 tachment of the four great longitudinal muscles ; and the well-known 

 lateral and median lines which have so long been a puzzle to ana- 

 tomists are, he says, in reality nothing more than intermuscular 

 developments of this layer. In some species each of the lateral lines 

 contains an axial vessel, though in very many others nothing of this 

 kind is to be met with. A periodical ecdysis of the chitinous por- 

 tion of the integument takes place in all Nematoids during the period 

 of their growth. 



The author agrees with Dr. Schneider as to the nature of the 

 transverse fibres attached to the median lines. They are contractile 

 prolongations from the longitudinal muscles, and may be considered 

 extrinsic muscles for the propulsion of the intestinal contents, since 

 the intestine itself has no muscular tissue in its walls. 



Schneider's description of the nervous system in Ascaris megalo- 

 cepka/a has been confirmed, and a similar arrangement has been re- 

 cognized by the author in several other Nematoids. It exists as a 

 nervous ring encircling the commencement of the oesophagus, in 

 connexion with many large ganglion-cells. The principal peripheral 

 branches are given off from the anterior part of the ring, and pro- 

 ceed to the region of the mouth and cephalic papillae. Although 

 well developed ocelli exist in many of the free marine species, no 

 nerve-filaments have yet been detected in connexion with them. 



The organs of digestion are mostly simple, the principal variations 

 being met with in the presence or absence of a pharyngeal cavity, 

 and in the structure of the oesophagus. In some species its parietes 

 are distinctly muscular, whilst in others, as in the Trichocephali 

 and Trichosomata, they are as distinctly cellular. Those possessing 

 a pharyngeal cavity sometimes have well-marked tooth-like processes 

 developed from its walls ; but the author believes that the chitinous 

 plates which are sometimes met with in posterior swellings of the 

 oesophagus are not " gastric teeth," as they have been hitherto de- 

 scribed, but rather valvular plates for ensuring greater perfection in 

 the suctorial process by which these animals pass their food along 

 this portion of the alimentary canal. 



The water- vascular system may be seen in many Nematoids in its 

 most elementary condition, as a small tubular gland, with an excretory 

 orifice in the mid- ventral region of the anterior part of the body. In 

 other Nematoids no trace of such a system exists ; whilst its most 

 developed condition yet recognized iu these animals may be seen 

 in Asccwis osculatu and A. spiculigera, where an intimate plexus of 

 vessels, still in connexion with an anterior ventral pore, is met with 

 in a peculiar development from the left lateral band. Intermediate 

 conditions between these extreme forms may be traced in other spe- 

 cies ; and from the obviously glandular nature of the tubular or 

 pyriform organ met with so commonly in the free, and also in many 



