158 COMPARATIVE ANATOMY 



certain points where it may be seen to pulsate in a rhythmic 

 manner. The waves of contraction advance and recede, but 

 gradually the advancing movement predominates, and little 

 prominences are formed, the basal part of each contracting 

 to form a stalk consisting of a tube of a tough hyaline substance 

 through which the protoplasm continues to flow till all the 

 contents of the neighbouring parts of the plasmodium become 

 aggregated on its summit in the form of a spherical mass. 

 The outer layer of this mass hardens and thickens to form 

 a wall surrounding the more fluid contents, and part of the 

 calcareous granules which were scattered through the plas- 

 modium are incorporated into the substance of the w r all. The 

 fluid contents become differentiated into two structures. First 

 a part of the protoplasm gives rise to a branching system of 

 flattened threads, spreading like a network from the base of 

 the chamber to its wall. The threads are expanded where 

 they unite together, and contain a number of lime granules 

 evenly distributed through their substance. The whole system 

 of branching threads is called the capillitium, and the remain- 

 ing mass of protoplasm filled with nuclei may conveniently be 

 named the sporoplasm. As yet no conjugation of nuclei prior 

 to spore formation has been observed in Badhamia, but in 

 Arcyria and some other Mycetozoa the nuclei of the sporo- 

 plasm have been observed to fuse together in pairs, forming 

 half as many conjugation nuclei or synkaryons. In each 

 synkaryon eight bivalent chromosomes make their appearance 

 and it is supposed, though the evidence is not very clear on 

 this point, that one moiety of each bivalent chromosome is 

 derived from one, the other moiety from the other, of the two 

 conjugating nuclei. A heterotypic or meiotic division then 

 takes place simultaneously in all the synkaryons, as a result 

 of which each is divided into two daughter-nuclei containing 

 eight univalent chromosomes. While the meiotic division is 

 in progress the protoplasm breaks up into a number of lobed 

 masses each containing from six to ten nuclei. Eventually 

 these masses are divided into as many corpuscles as there 

 are nuclei. Each corpuscle containing a -single nucleus is 

 a spore : it acquires a cell-wall composed of a substance 

 resembling the cutin of cuticularised vegetable cells, and a 

 period of rest ensues. Each globular chamber borne on its 

 stalk is called a sporangium. The sporangia of Badhamia 



