86 THE INVERTEBRATA 



gametes of each undergo cross-conjugation with those of the other, 

 or there is one cross-conjugation and the remaining gamete of each of 

 the two original individuals performs parthenogenesis. In fresh and 

 marine waters. 



Actinosphaeriutn (Fig. 33). Unprotected; with many nuclei, 

 against which the central filaments of the axopodia do not end. In 

 preparation for autogamy the nuclei are reduced in number and the 

 cytoplasm divides into as many corpuscles as there are nuclei. Each 

 of these then undergoes a process similar to that which occurs in 

 Acttnophrys, forming a zygote which hatches as an independent 

 individual. In fresh waters. 



Clathrulina (Fig. 8). Animal enclosed in a stalked, pseudochi- 

 tinous lattice sphere; one nucleus. At binary fission, one product 

 becomes a biflagellula and swims away. In fresh waters. 



Order MYCETOZOA 



Plasmodial Sarcodina, living usually in damp places on land ; which 

 have in the active phase no shell, skeleton, or central capsule, but in 

 the quiescent phase a cyst of cellulose; possess numerous, blunt 

 pseudopodia; and are usually distributed by air-borne, cellulose- 

 coated spores. 



The life history of a typical mycetozoon is as follows. The adult 

 Plasmodium is a sheet of protoplasm containing many thousands of 

 nuclei and numerous contractile vacuoles. In it there are to be seen 

 veins along which streaming takes place, alternately towards and 

 from the periphery. It feeds in a holozoic manner, usually upon de- 

 caying vegetable matter, sometimes (Badhamia) on a living plant. In 

 drought it breaks up into numerous multinucleate cellulose cysts 

 which constitute the sclerottum. It prepares for reproduction by 

 condensing at certain points, at each of which it forms a cellulose spo- 

 rangium, often stalked. In the sporangium is a capillitium of cellulose 

 threads and entangled in the capillitium are uninucleate, cellulose- 

 coated spores, whose formation is preceded by a reduction division. 

 When the sporangium is ripe it bursts and the spores are dissemin- 

 ated by wind, etc. In damp surroundings they open and liberate each 

 an amoebula which becomes a flagellula. The flagellulae perform 

 syngamy and the zygote again becomes an amoebula. The amoebulae 

 tend to fuse and form small plasmodia. By multiplication of their 

 nuclei the adults arise. 



Chondrioderma (Fig. 73). On bean stalks. 



Badhamia. On fungi, especially Stereum. 



Plasmodiophora. In turnips, causing " finger-and-toe " disease. No 

 sporangia. Distribution by flagellulae in soil. 



