7O J. F. McCLENDON. 



VII. RELATION OF PRESSURE, ETC., TO THE TYPE OF CLEAVAGE. 



When the eggs are released from the oviduct in sea water, 

 they begin slowly to round up and separate one from another. 

 The eggs adhere together so strongly that their tendency to 

 assume a spherical form is greatly impeded, and it always takes 

 several hours for them to round up. The majority of the eggs 

 liberated begin to disintegrate before they proceed very far toward 

 becoming isodiametrical. This is due to their very low surface 

 tension, their cohesion being less than their adhesion for the 

 surface film of sea water or for glass. This is shown by the fact 

 that the eggs tend to stick to the bottom of the glass dish con- 

 taining the sea water, and when the dish is tilted so that some 

 eggs come in contact with the surface of the water, they quickly 

 spread out over that surface. All these experiments support 

 the direct observation that the oocyte is surrounded by no other 

 membrane than its surface film. 



If eggs are left standing in sea water more than two to four 

 hours their surfaces begin to disintegrate. This is probably caused 

 by partial solution in sea water. The nuclei remain intact after 

 a great deal of the egg has disintegrated. If the eggs are placed 

 in hypotonic solutions they swell, if in hypertonic solutions, they 

 shrink, without any other change that can be observed. I tried 

 solutions of magnesium chloride, ether, and sodium hydroxide, 

 of varying strengths in sea water containing eggs alone 01 eggs 

 and sperm but could neither induce parthenogenesis nor fertiliza- 

 tion. The spermatozoa are very similar to those of cirripedia, 

 being thread-like and each containing a homogeneous thread of 

 chromatin running the entire length. The sperm of many crus- 

 tacea are non-motile when examined in sea water or serum, but 

 some of them have been observed to perform movements in the 

 female genital ducts. Cano ('93) saw decapod spermatozoa 

 move lively in the Rec. seminis. It is therefore probable that I 

 did not find the proper stimulus to cause fertilization in sea 

 water. Immediately after fertilization and passage into the egg 

 strings the egg secretes a chitinous chorion that resists all 

 attempts at freeing the eggs so that they will round up, without 

 mutilating them, so I had to resort to looking for eggs that by 

 accident were not flattened in the usual manner. In the Di- 



