I SYNGAMY GAMETES — ZYGOTE 3 3 



talce place when soluble material has been provided in this way for the 

 growth of the young shoots. We have also reason to believe that these 

 ferments are only formed by the degradation of the protoplasm itself. Now 

 obviously this degradation must be very slow in a resting organism ; and 

 any external stimulus that will tend to protoplasmic activity will thereby 

 tend to form at the same time the digestive ferments and dissolve the stored 

 supplies, to render them available for the life-growth and reproduction of 

 the being. We now see why inactive " miserly " cells so often pass into a 

 resting state before dividing, and why they go on dividing again and again 

 when once they re-enter upon an active life, the living protoplasm growing 

 at the expense of the reserves.^ Besting cells of this type occur of course 

 only at relatively rare intervals in the animal-feeding Protozoa, that have to 

 take into their substance the food they require for their growth and life- 

 work, and cannot therefore store up much reserves. For they are constantly 

 producing in the narrow compass of their body those very ferments that 

 would dissolve tlie reserves when formed. Internal parasites and " sapro- 

 phytes," that is, beings which live on dead and decayed organic matter, on 

 the other hand, live surrounded by a supply of dissolved food ; and rarely 

 do we find larger cells, richer in reserves, than in the parasitic Sporozoa, which 

 owe their name to the importance of brood -formation in their life-history. In 

 Eadiolaria (p. 75 f.) a central capsule separates off an inner layer of protoplasm ; 

 the outer layer is the one in which digestion is performed, while the inner 

 layer stores up reserves ; and here brood-formation appears to he the rule. - 

 But the largest cells of all are the eggs of the Metazoa, which in reality lead 

 a parasitic life, being nurtured by the animal as a whole, and contributing 

 nothing to the welfare of it as an individual. Their activity is reduced to 

 a minimum, and the consequent need for a high ratio of surface to volume 

 is also reduced, which accounts for their inordinate size. But directly the 

 reserve materials are rendered available by the formation of a digestive 

 ferment, then protoplasmic growth takes place, and the need for an extended 

 surface is felt ; cell-division follows cell-division with scarcely an interval in 

 the process of segmentation. 



Syngaihy.^ — The essence of typical syngamy is, that two cells 

 ("pairing-cells," "gametes") of the same species approach one 

 another, and fuse, cytoplasm with cytoplasm, and nucleus with 

 nucleus, to form a new cell (" coupled-cell," " zygote "). This process 

 is called also "conjugation" or "cytogamy." In the simplest 

 cases the two cells are equal and attract one another equally 

 ("isogamy"), and have frequently the character of zoospores. 



In an intermediate type, the one cell is larger and more 

 sluggish (female), " megagamete," " oogamete," " oosphere," " egg " ; 

 the other smaller, more active (male), " microgamete," " spermo- 

 gamete," " spermatozoon," " sperm " ; and in the most specialised 



' See Hartog in Rep. Brit. Ass. 1896, p. 933, 1900, p. 786. 

 2 Commonly called "fertilisation," or "sexual union," inadequate and mis- 

 leading terms. 



VOL. T ^ 



