206 



GENERAL BIQL 



,oc,v 



Fig. 97. 

 Volvox Globator, a Colonial Form of the Volvocaceae. 



(See Fig. 49, where this same form is considered an 

 animal.) 



A, mature colony, with four daughter colonies devel- 

 oping in its interior ; B, section of the edge of the colony, 

 snowing three vegetative cells and a developing egg ; 

 C, a packet of sperms within the parent cell and a single 

 sperm very much magnified at the side ; D, an egg sur- 

 rounded by a swarm of sperms ; E, an oospore with 

 heavy protective wall. (From Bergen & Davis' "Princi- 

 ples of Botany," by permission of Ginn & Co., Pub- 

 lishers. ) 



ago Spallanzani succeeded 

 in artificially fertilizing eggs 

 of various animals ; but more 

 recently several workers 

 have succeeded in causing 

 the egg to begin growing by 

 chemical means. These men 

 saw that the formation of 

 the fertilization-membrane is 

 purely physical, so biologists 

 began to reason that it ought 

 to be possible to induce it 

 artificially. The experiment 

 was first successfully made 

 by a zoologist, Loeb, with 

 the eggs of sea-urchins and 

 other marine animals. In 

 1913 it was successfully accomplished by Overtoil with the eggs of 

 Fucus. The eggs were dipped for about a minute, or a minute and a half 

 to two minutes, in a mixture of 50 cc. of sea-water plus 3 cc. of a very 



weak solution of acetic, butyric, or 

 other fatty acid, and then trans- 

 ferred to normal sea-water. This 

 treatment caused the formation of 

 the fertilization-membrane, quite as 

 in natural fertilization by the sperm. 

 If, after the formation of the mem- 

 brane, the eggs are placed for 30 

 minutes in hypertonic sea-water 

 (50 cc. of normal sea-water plus 8 

 to 10 cc. of a weak solution of so- 

 dium chloride (common salt), or 

 potassium chloride), and then back 

 into normal sea-water, the eggs be- 

 gin to divide and continue to de- 



Fig. 99. Phycomycetes. 



These are the alga-like fungi without septa 

 in the mycelium, except in the sporing 

 branches, where they occur to cut off the spore- 

 bearing cells. The septa also occur in old 

 filaments. The mycelium is therefore continu- 

 ous. 



Common water mold (Saprolegnia.) : A, 

 a. fly from which mycelial filaments of the par- 

 asite are growing ; B, tip of branch organized 

 as a sporangium ; C, sporangium discharging 

 biciliate zocispores ; F, oogonium with an- 

 theridium in contact, the tube having pene- 

 trated to the egg ; D and E, oogonia with 

 several eggs. (A-C after Thuret ; D-f after 

 De Barry.) 



Fig. 98. Growth Habit of the Bread Mold 



( Rhizopus Nigricans ) . 



Sketch showing two groups of erect hyphae 

 bearing sporangia, with root-like clusters of 

 filaments at their bases. 



