i jo 



THE ANIMAL PARASITES OF MAN 



The discovery of amoeboid germs in the pseudonavicellae by Lieberkiihn (1855) an ^ 

 the demonstration of myonemes further aided in the elucidation of their true 

 systematic position. The entire process of conjugation, of which Du four had seen 

 one phase, was followed by Giard under the microscope. 



From 1873 onwards Aime Schneider made important additions to the knowledge 

 of the morphology, life-history, and systematic position of numerous gregarines. 

 Biitschli (1881) and L. Leger (1892) also contributed much work on the subject. The 

 discoveries of Schaudinn with regard to the life-cycle of Coccidia gave a fresh 

 stimulus to the study of the Gregarines, whereby the life-cycles of numerous forms 

 and the phases thereof have been elucidated. 



Asexual multiplication is not common among the Gregarines, but is known to 

 occur in the sub-order Schizogregarinea, formerly known as the Amcebosporidia. 



Although the Gregarinida are not known to be parasitic in man or other verte- 

 brates, they are of great interest, inasmuch as they are among the earliest known 

 Sporozoa, and therefore will be briefly described here. 



The Gregarines are usually elongate, somewhat 

 flattened organisms (figs. 59, 60), whose bodies are 

 enclosed in an elastic and often thick cuticle. The 

 enclosed living substance shows a separation into 

 ectoplasm and endoplasm, as is common among 

 Protozoa. The cuticle is sometimes regarded as the 

 outer portion or epicyte of the ectoplasm. A single, 

 vesicular, spherical, or elliptical, large nucleus, with 

 its chromatin concentrated to form a spherical 

 karyosome, is present. The body of some gre- 

 garines may be divided by ingrowing ectoplasmic 

 partitions or septa, and are then said to be " septate " or 

 "polycystid" (fig. 61). Other gregarines remain simple and non-septate, 



FIG. 59. Monocystis 

 agilis from seminal 

 vesicles of Lumbncus 



X 250. (After Stein.) 



FIG. 60. Gregarina longa fiom larva of crane-fly (Tipula). a, in epithelial cell of host ; 

 b, c, gradually leaving host-cell ; d, adhering to host-cell ; e, fully developed free tropho/.oite. 



and are termed "monocystid" (fig. 59). The monocystid gregarines 

 occur especially in the body cavity of Chaetopoda and Insecta, more 

 rarely in Echinodermata, in the parenchyma of Platyhelminthes, 



