3 o8 



POPULAR SCIENCE MONTHLY. 



Among the Chaetophoraceae is the genus Aphanochaete (see Fig. 

 4), presenting one of the most interesting stages of sexual evolution 

 and bridging over a very important gap. Aphanochaete develops its 

 female gamete singly in a mother cell. It is discharged into the 

 water surrounded by a delicate vesicle. The gamete, although very 

 large, is ciliate. However, it moves about scarcely at all, and does 

 not leave the vesicle. The sperms gather around the dissolving 

 vesicle, and finally one pierces it and fuses with the female gamete. 

 The fertilized egg immediately begins to turn on its axis and 

 moves about in the water for a few moments and then settles 

 down to rest. It is probable that the cilia remain on the egg for 

 this short period of motility, but it is evident that the female 

 gamete has entirely given up the free-swimming habit. But what is 

 more important, the oogonium appears to deliver its gamete with 

 reluctance, for it is not entirely freed from its investing membrane 



Fig. 4. Aphanochaete repens ; a, antheridia; b, oogonia ; c, sperms; d, eggs. (After 

 Huber.) 



until after fertilization. It would be but a small step for Aphano- 

 chaete to retain this female gamete in the oogonium as a motionless 

 egg and thereby present the furthest extreme of heterogamy. Such 

 a condition would place Aphanochaete very close to Coleochaete, which 

 it strikingly resembles in some important respects. 



The last form in this series of green algae is Coleochaete, the sole 

 representative of the family Coleochaetaceae. Of all the algae this 

 type probably stands the closest to the liverworts, not because its sexual 

 organs are similar, but because it presents a sphorophyte generation 

 resembling that of the lowest liverworts (Eicciales). Coleochaete is 

 heterogamous, but its sexual organs can scarcely be compared with 

 the archegonia and antheridia of the Bryophytes. These structures 

 are to be related only with the greatest difficulty to the sexual organs 

 of the algae, and probably not through any existing type of structure, 

 unless it be the organ called the plurilocular sporangium. 



