84 BASIC METHODS FOR EXPERIMENTS 



the resting stage or in a phase of mitosis. The sperm after 

 entry may or may not be accompanied with astral configurations. 

 When present the aster may or may not contain a central 

 granule, the centriole. (Centrloles may be seen in some living 

 eggs, as Breslau has shown.) 



(i) Eggs which are enclosed in jelly before fertilization: 

 Echinids, starfish, Cumingia, etc. 



Eggs which extrude jelly after fertilization: The genera 

 Nereis and Platynereis. 



(2) Eggs with most pronounced membrane-separation: Echi- 

 nids, Asterias, Nereis; with least: Chaetopterus, Cumingia. 



(3) Egg with most pronounced changes in shape after fertili- 

 zation: Nereis limhata. To a less degree: Echinids. 



(4) Eggs with micropyles: Loligo, teleosts. (The funnel in 

 the jelly of echinid eggs is not a micropyle!) 



Eggs Into which spermatozoa enter at a fixed point: Ciona, 

 Amphioxus, and usually Chaetopterus. 



(5) Eggs with most persistent fertilization cones in the order 

 named: Nereis, Echinarachnius, Arbacia. 



(6) Eggs whose nuclei show no astral formation at the time 

 of fertilization: Those fertillzable in the stage of the intact 

 germinal vesicle; Ciona, Molgula; and echinids. In Ciona and 

 Molgula, the maturation spindles present are anastral; in the 

 echinids, the resting nucleus shows normally no radiations until 

 apposition of the sperm nucleus. 



(7) Eggs in which the sperm nucleus shows no asters: 

 Trematodes. 



(8) Eggs in which the sperm nucleus is accompanied by an 

 aster without centriole: Echinids. With a centriole: Nereis, 

 Chaetopterus. 



