THE SPOROZOA 



3'5 



Genus 2. Siedleckia, Caullery and Mesnil, 1898, for S. nematoides, 

 C. and M., parasitic in the digestive tract of Scoloplos miilleri and Aricia 

 latreillei. It occurs as a minute, worm-like creature (Fig. 126), attached by 

 one extremity, termed proximal, to a cell of the intestinal epithelium. 

 The body hangs free in the lumen of the gut, and performs various 

 movements of torsion and flexion. Sometimes individuals are found 

 unattached and progressing freely. The youngest stages are spindle- 

 shaped and slightly curved, resembling sporozoites, with one or two nuclei 

 (Fig. 126, a). As they grow in length the nuclei increase in number, 

 keeping at first in single file (Fig. 126, b-d), but later forming several rows 

 at the distal extremity of the body (Fig. 126, e). The full-sized parasite is 



d, 



Fio. 126. 



Phases of the life-cycle of Siedleckia nematoides, Caull. and Mesn. (par. Scoloplos miilleri, etc.). 

 a, young stage, with two nuclei ; b, c, d, older stages, with nuclei (n) still in .single file ; in d 

 some of the nuclei are commencing to elongate in a transverse direction ; e, full-grown in- 

 dividual, with very numerous nuclei ; /, inultinucleate spheres cut off from the distal extremity 

 of a parasite such as shown at e ; in g the sphere is commencing to grow into a vermiform 

 Siedleckia. (After Caullery and Mesnil.) 



about 150 p in length and continues to elongate, but as it does so, small 

 spherical segments, containing a variable number of nuclei, are constricted 

 off from the distal extremity and detached (Fig. 126, /, g). Each of these 

 becomes a young Siedleckia. No other method of reproduction has been 

 observed. 1 The facts upon which to form a judgment with regard to the 

 affinities of Siedleckia are therefore somewhat scanty. Labbe [130c] con- 

 siders it allied to the Mesozoa, but it is difficult to see why. The general 

 habitus of the animal is more like a Gregarine than anything else, and 

 Caullery and Mesnil [86] have noted its resemblance to the vermiform 

 Gregarines, such as Selenidium, occurring in Annelids. The general 

 description of Siedleckia and its reproduction reads (at least, to one who 

 has not seen either of these forms) remarkably like the description of the 



1 It is by no means apparent bow the multinucleate spheres detached as describe 

 become the young forms with two or three nuclei, or whence the latter originate. 



