GIO DR. II. CIIABLTON BASTIAN OX TUB ANATOMY AND PHYSIOLOGY 



the smallest germ upwards, at periods when the parent must have been actually within the 

 cellular tissue of the human body for no less than eight, nine, or even more months*. 



In all the species of the genus Dorylaimus, before the animals have attained their full 

 adult size, a reserve spear may always be obsci-ved imbedded in the anterior portion of the 

 oesophagus, just posterior to the one in situ and slightly larger than it. This reserve 

 spear seems to have no special connexions of any kind ; it appears to be simply lodged 

 in the substance of the oesophagus, and not even a containing sac can be detected. In 

 the progress of growth of the animal the reserve spear gradually approximates to the 

 position occupied by the other, and at last displaces it, as the permanent tooth supplants 

 its temporary predecessor. What causes the reserve spear to rise, or how the movement 

 is effected, I am quite unable to say. Neither do I know how many times a spear is 

 thus displaced during the progi-ess of the animal towards maturity. Being of a homy 

 nature and cylindrical in form, it is perhaps itself incapable of growth, and therefore 

 spears of successively larger size ai-e produced, to keep pace with the increasing dimen- 

 sions of the animal. 



From what I have seen of the anatomy of that form of the so-called Filaria piscium 

 infesting the common Haddock, I am quite convinced that it really is most closely 

 allied to A. osculata and A. spiailigera, which should all be placed, if not under a new 

 generic name, certainly apart as a distinct subgenus. At the same time that I obtained 

 the encysted Nematoids from beneath the peritoneal membrane of the Haddocks, I also 

 dissected a mackerel, and having found one similar encysted animal entangled amongst 

 its pyloric caeca, I then opened the intestinal canal, and found within it a single Nema- 

 toid entirely free and unencysted. This was half as large again as the largest of the 

 animals found beneath the peritoneal membrane, though when submitted to the micro- 

 scope it was found to be a more highly developed individual of the same species, and 

 quite devoid of the membranous sheath-like covering with which the others were closely 

 enveloped. Although this aniinal did not exhibit the three head lobes at all jjlainly, 

 the four papillaj usually situated on them were distinct. The development of the lobes 

 is therefore probably characteristic of a later period of the animal's growth. The 

 genital organs, if present, must still have been in a very rudimentary condition. How 

 are we to suppose this animal gained access to the intestine of the mackereK It 

 seems probable that this occurred either owing to the mackerel having swallowed 

 some smaller fish in which the Nematoid existed in an encysted state (in which case 

 we might expect the mackerel to be the proper host of this species in its mature con- 

 dition), or else we must have recourse to the more improbable alternative, that one of 

 the encysted individuals, previously to be found beneath the peritoneal membrane, had 

 contrived in some way to penetrate the wall of the intestine in order to gain that situa- 

 tion requisite for its future development. 



The development of the genital organs does not seem to take place veiy early. Spe- 



* Professor Let7ckaet has accepted ttis doctrine, since it seems most in harmony with anatomical facts, and 

 also best explains certain peculiarities in the life-history of this parasite. 



