Centrifugal Force upon Beetles' Eggs 54 ^ 



polar areas includes a specially modified protoplasmic area proba- 

 bly comparable to a polar ring." Conklin ('05,(3, p. 211) says 

 of the Ascidian egg (Cynthia) : "All the principal organs of the 

 larva in their definite positions and proportions are here marked 

 out in the 2-cell stage by distinct kinds of protoplasm," and again 

 on p. 216 this author states that "the substances of the ectoderm, 

 mesoderm and endoderm are recognizable in the unsegmented 

 egg." In another place (Conklin '05, h, p. 220) we find the state- 

 ment that, "Three of these substances are clearly distinguishable 

 in the ovarian egg and I do not doubt that even at this stage they 

 are differentiated for particular ends." 



Many other eggs that do not exhibit a normal stratification and 

 are apparently homogeneous throughout take on a zone-like 

 appearance under the influence of a strong centrifugal force. 

 Morgan ('06) found that w^hen the unsegmented eggs of Rana 

 sylvatica are revolved 1600 times per minute for seven minutes 

 the pigment and yolk are driven to the top of the egg, leaving a 

 clear polar field. Similar results were obtained in toads' eggs 

 in three minutes. Lyon ('06, '07) was able to induce four layers 

 in the egg of the sea-urchin, Arbacia. Two layers were obtained 

 in eggs of the starfish, Asterias (Lyon, '07). The annelid, Chae- 

 topterus, exhibited three layers. The same author also centri- 

 fuged the eggs of the Ascidian, Cynthia, the Gephyrean, Phascolo- 

 soma, and the common garden spider; the eggs of Cynthia and 

 Phascolosoma were stratified into three layers, those of the spider 

 into two. LilHe ('06) found that not only in the unsegmented 

 eggs of Chaetopterus but also in the two, four and eight celled 

 stages three zones appeared in each cell when placed under the 

 influence of centrifugal force. The contents of the egg of the 

 mollusk, Cumingia, may be separated into three zones (Morgan, 

 '08). 



The eggs of the rotifer Hydatina senta were centrifuged by 

 Whitney ('09) while still within the mother. Three distinct 

 layers resulted : a pink zone, a clear middle zone and a gray zone. 



The eggs of Calligrapha bigsbyana are when laid of a nearly 

 uniform pale-yellow color. When subjected to a strong centri- 

 fugal force for a sufficient length of time three zones are distin- 



