CHAPTEK LX. 



THE GREGARINIDA. 



[THE Gregarinida are an Order of the Sub-division Telosporidia of the 

 Sporozoa (see p. 760).] 



The Gregarines are unicellular parasites which live in the gut or body 

 cavity of the invertebrata and especially in the articulata. [They are wholly 

 or in part intra-cellular parasites inhabiting usually the epithelial cells of 

 the host, but never the blood cells.] 



In the adult form [Trophozo'ite] they are more or less elongated structures 

 measuring from 10-20/x to 16 mm. and consist of a continuous outer membrane 

 or cuticle (epicyte) containing an ectoplasm, endoplasm and a nucleus. The 

 body of a Gregarine may be homogeneous or segmented hence the two groups 

 monocystida and dicystida. In the dicystida the segments are generally 

 unequal in size ; the anterior segment or head is known as the protomerite 

 and in some cases possesses an organ of attachment, the epimerite ; the 

 posterior segment or body known as the deutomerite contains the nucleus. 



The cuticle or epicyte frequently shows longitudinal striae composed of 

 myonemes. Transverse striation is less commonly seen. 



The cytoplasm consists of an ectoplasm and endoplasm the latter as a rule 

 containing a large number of chromatic granules. 



The nucleus, usually single^ is spherical or oval and has several nucleoli. 



Those Gregarines which have an epimerite remain attached for some time 

 to an epithelial cell of the host then by rupture of the junction between the 

 epimerite and protomerite the parasite becomes detached and is free. 



The Gregarines exhibit movement, sometimes of translation and some- 

 times of flexion : movements of flexion are limited to the deutomerite and 

 are accompanied by active contractions of the protoplasm. 



At a given moment in its life history the Gregarine becomes encysted, 

 whether it has had previous association with another of its kind or not. 



In this association which is not a conjugation but merely a juxtaposition 

 two individuals become attached together [syzygy] either by their anterior 

 ends as is the case with but few exceptions in the Monocystids or by opposite 

 ends as in the Dicystids. [The two associated individuals then generally 

 become surrounded by a common membrane.] In Gonospora longissima 

 Caullery and Mesnil have shown that the septum between the two associated 

 individuals is destroyed and that the protoplasm of the parasites fuses. 

 Occasionally a number of individuals become attached end to end forming 

 a chain. 



[After encystment l the nuclei of the two trophozoltes or sporonts or gameto- 



t 1 See Professor Minchin's description in A Treatise on Zoology edited by E. Ray 

 Lankester, London, 1909.] 



