22 



POPULAR ILLUSTRATIONS OF 



the "Annal.de Sci. Nat." vii., 1837, down to Kolliker's " Icones 

 Hist.," 1864, they have been well examined by naturalists, and some 

 very curious features in their economy discovered. At first about 

 eighty species were named and divided into genera. It was, how- 

 ever, found that many of the forms thought to be specifically 

 distinct were only the different phases of the metamorphoses which 

 the animal undergoes in its reproduction. These changes I will 

 describe. 



Fig. 10. 



Fig. 11. 



Fig. 17. 



Fig. 16. 



Fig. 10. Gregarina nemertis (Koll.), highly magnified a, nucleus, containing nucleolua 

 6, cell wall c, granular contents of cell. 



Fig. 11. Two Gregarinse united together. 



Fig. 12. The same, contracted. 



Fig. 13. The same, forming cell wall, and nucleolus disappearing. 



Fig. 14. Nucleus divided and enlarged. 



Fig. 15. Further division of nucleus, and formation of " cyst membrane " (d). 



Fig. 16. Same cell, containing " navicular "-shaped bodies, and band of division dis- 

 appearing. 



Fig. 17. Same, cell, containing matured larvse of Qregarinae, band of division and cyst 

 membrane entirely gone (alter Kolliker). 



First, two of the elongated cellular nucleated creatures shown at 

 Fig. 10, having become obtuse at the extremity nearest the nucleus 

 (a), come into contact with each other, as shown in Fig. 11. The 

 extremities then contract, and the next transformation is shown in 

 Fig. 12, where it will be seen they have become firmlv united into 



