ARTICLE XVI. 



Some Observations on Nematoidca Imperfecta, and Descriptions of three Parasitic Infusorise. 



By Joseph Leidy, M. D. 



From the obscure position in which cntozoa are usually found, but little, comparatively, 

 is known of the continuous history of any of them, and at present it is a quite prevalent 

 opinion among hclminthologists, from observations made upon several species of Distoma, 

 that these beings pass through different stages of their existence — sometimes within an 

 animal, at other times without the animal, or within several different animals. If this is 

 the case, it becomes important to present all observed facts in connexion with the develop- 

 ment of entozoa, and it is upon such considerations that I have presented the following 

 description of some nematoid entozoa in an imperfect stage of development, or in a stage 

 where no trace of generative apparatus is observable. 



1. Nematoidcum cavitatis abdominis Passali cormili, (PI. 11, figs. 42-45.) — This worm is 

 found in the abdominal cavity of the Passalus cornulus, among the intestines and rote adiposa 

 in about nine-tenths of the insects. It is met with frequently in great numbers; I have in 

 my collection a vial containing over 5000, obtained from not more than 40 insects. Some- 

 times not over half a dozen are found, at others as many as 500 may be discovered in a single 

 insect The worm is usually curved vcntrally, and exhibits but little motion until placed in 

 water, when it becomes quite active, wriggling about for twenty-four hours or more. 



It is about 1| lines long, but varies from 1 to 2 lines, and is about 1.150th of an inch 

 wide. The colour is white, opaque ; occasionally one or two will be found which arc more 

 or less brown or even black, but otherwise they do not differ cither in construction or form. 



The form is cylindrical, moderately narrowed toward the extremities; anteriorly trun- 

 cated, posteriorly rounded, and terminated by a short, acute epidermal spine. 



The structure is simple, exhibiting within the integument nothing but an alimentary 

 canal and intervening granular matter. 



The integument is thin, strong, clastic, transparent, and colourless. It presents a very 

 faint appearance of being finely annulated. 



The mouth is round, large, and surrounded by a slightly lobed margin or lip. 



The pharynx is short, cylindrical, presents several longitudinal striffi, and opens into a 

 long, wide, cylindrical oesophagus. The latter is but faintly outlined from the general 

 granular structure of the body. It appears to have several longitudinal folds, and at its 

 commencement has a yellowish coloured structure, (pi. 11, 6g. 15.) apparently corneous, 

 composed of oval or oblong lobes placed side by side around the commencement ol the 

 o'sophagus. The ventricular intestine is white, opaque, cylindrical, a little less than the 

 breadth of the cavity of the body, and in length extending to the anal aperture, lis into- 



