ALG^. 219 



by its rupture. Several generations of families endowed with motion are formed in 

 this manner one after another. The succession of these generations is sometimes 

 interrupted by the formation of Micro-gonidia ; i.e. of small swarm-spores, which, 

 resulting from repeated division of the primordial cells of a family, become completely 

 isolated and dispersed. They are furnished with four vibratile cilia and each, secreting 

 a cell-wall, finally passes into a roundish resting-cell, the fate of which is still un- 

 known (Fig. 155, XIT, XIII, XIF). The succession of generations of motile families 

 is brought to an end by the formation of resting-cells. The separate primordial cells 

 of the last motile family lose their cilia, and surround themselves with a firm 

 closely- adherent cell-wall ; they then resemble the cells of Protococcus, and are Hke the 

 resting-cells which proceed from the small swarm-spores of Hydrodictyon. They accu- 

 mulate at the bottom of the water, and there grow into larger green balls (Fig. 155, /), 

 the colour of which passes over, when mature, into red. Only when these resting-cells 

 have remained dry for a long time are they in a condition, when again moistened, to 

 develope gradually generations endowed with motion ; their contents divide into two, 

 four, or sometimes eight parts, which, after absorption of the cell-wall, set up a motion 

 as swarm-spores with two cilia (Fig. 155, 77, 777, IF). In the course of the day they 

 surround themselves with a separable cell-wall, and in this condition the unicellular 

 swarm-spores (Fig. 155, F, FI, FII) resemble those of the genus Chlamydococcus. After 

 some hours each of these swarm-spores divides into two, four, or eight daughter-cells, 

 which, lying in one plane, secrete a common cell-wall, and each developes two cilia ; 

 they then separate from one another, but remain enclosed in the common spherical 

 cell- wall which has now separated itself from them^. After absorption of the mother-cell- 

 wall the new family endowed with motion thus becomes free (Fig. 155, FII b, Fill, IX, 

 X), grows in the course of the day, and forms in the night eight new similar families. 



After Cohn and Carter had already detected phenomena in certain Volvocineae (Volvox 

 and Eudorina), which pointed to sexual union, Pringsheim has recently proved this to 

 be the case with certainty in Pandor'ma morum, one of the commonest species. The 

 sixteen cells of a family of Pandorina are closely crowded together, and surrounded by 

 a thin gelatinous envelope out of which the long cilia project. The asexual multipli- 

 cation results from the formation of a new sixteen-celled family in each cell of the 

 mother-family ; and the sixteen daughter-families become free by the absorption of the 

 gelatinous envelope of the mother-family. The sexual reproduction is brought about in the 

 same kind of way though with some points of difference ; the gelatinous envelopes of the 

 young families become softened, and the separate cells are thus freed and move each with 

 its two cilia ; these free swarm-spores are of very variable size, rounded and green at the 

 posterior end, pointed hyaline and furnished with a red corpuscle in front, where they 

 bear the two cilia. Among the crowd of these swarm-spores may be seen some which 

 approach in pairs as if they were seeking one another. When they meet, their points 

 come in contact, and they coalesce into a body at first biscuit-shaped, but gradually 

 contracting into a ball ; in this ball the two corpuscles are still to be seen, the hyaline 

 part is relatively large, and both pairs of cilia are still present ; but these all soon dis- 

 appear. These processes last for some minutes. The green ball which results from 

 the conjugation is an Oospore, and germinates only after a long period of rest. If the 

 oospores, when dried up and of a red colour, are placed in water, the development 

 begins after twenty-four hours ; the exospore breaks up, as in Hydrodictyon ; an inner 

 membrane swells up like a bag, and allows the protoplasmic contents to escape in the 

 form of a swarm-spore (more rarely after division into two or three). These swarm- 

 spores which proceed from the oospore surround themselves with a gelatinous envelope, 

 split up by successive divisions into sixteen primordial cells, and thus form new Pando- 

 rina-families. 



» [Archer has described, /. c, pp. 7, 8, a remarkable amceboid phase which the primordial cells 

 of Stephanosphtera undergo. — Ed.] 



