SEXUAL PHENOMENA IN THE PROTOZOA 



225 



established in a great many Protozoa, especially among the colonial 

 forms of Mastigophora, and, to a less extent, in Sarcodina and in 

 some Sporozoa. In the Sarcodina, macro- and microgametes are 

 formed by many marine types, including Reticulariida and Radiolaria, 

 and Brady, Brandt, and Haeckel do not hesitate to say that sexual 

 reproduction is brought about by their union. In only one case, how- 

 ever (Hyalopus), has conjugation been actually observed. Here the 

 cell-body spontaneously fragments into isogamous microgametes 

 which swim away from the shell and conjugate (Schaudinn). In the 

 Sporozoa, also, the recent results obtained by Siedlecki ('99) show an 



D 



B 



Fig. 123. — Conjugation in Cklorogonium euchlorum Ehr. [STEIN.] 

 A. Adult individual. B. Macro- and C. microgamete formation. D. Conjugation. 



analogous phenomenon, and at the same time they throw considerable 

 doubt upon Wolters's ('91) conclusions that the nuclei of two conju- 

 gating Gregarines unite. 1 According to Siedlecki, two similar in- 

 dividuals of Monocystis ascidice come together and secrete a common 

 cyst within which they sporulate, each individual by itself. There 

 is no union of nuclei as in Actinophrys, nor interchange of parts 

 of nuclei as in the. Infusoria, but the nuclei rapidly divide, and 

 the subdivisions ultimately become the nuclei of minute cells resem- 

 bling spores. These have been repeatedly observed in Gregarinida, 



iCf.p. 157. 



