372 Mr. Bastian Anatomy and Physiology ofNematoids. [June 15, 



Schneider's description of the nervous system in Ascaris megalocephala 

 has been confirmed, and a similar arrangement has been recognized by the 

 author in several other Nematoids. It exists as a nervous ring encircling 

 the commencement of the oesophagus, in connection with many large 

 ganglion-cells. The principal peripheral branches are given off from the 

 anterior part of the ring, and proceed 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 con- 

 nexion 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 described, 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 Nema- 

 toids no trace of such a system exists ; whilst its most developed condition 

 yet recognized in these animals may be seen in Ascaris osculata 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 species ; and from the obviously glandular nature of the 

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

 many of the parasitic species, he thinks considerable light is thrown upon 

 the function of the " water- vascular " system. He says, " Here we have 

 undoubtedly to deal with an excretory glandular apparatus. No one 

 could for a moment regard these structures as at all analogous to vessels 

 destined alternately to receive and discharge an external fluid medium. I 

 believe that in the Trematoda and Teeniada also, where similar though 

 often more developed systems exist, their function is in like manner one of 

 a purely eliminatory kind ; and 1 therefore cannot but look upon the 

 name of ' water-vascular ' apparatus as a singularly inappropriate appella- 

 tion for this system of vessels." 



Other very peculiar transverse vessels exist in the deep integumental 

 layer of Ascaris megalocephala and ^4. lumbricoides, mostly running in pairs 

 from median line to median line, and, strangely enough, being about twice 

 as numerous on the right as on the left side of the body. 



The author believes that in the Nematoids but little provision exists for 



