550 FRANK R. LILLIE 



an acid (aggregation) and also an alkali (agglutination) on the 

 spermatozoa. The comparison may, of course, be superficial, 

 but it serves at least to emphasize the double action of the egg- 

 secretion. 



As contrasted with the difference in rapidity and delicacy of 

 reaction between the spermatozoa of Nereis and those of Arbacia 

 to inorganic substances, we may note in advance that the reactions 

 to the egg extractives are as rapid and clear in the one case as in 

 the other, and are entirely similar in principle, though there are 

 certain secondary differences that will be noted in the proper 

 place. 



2. INITIAL EXPERIMENT 



We may begin by describing the reactions to be observed in 

 the case of an Arbacia sperm-suspension freshly made and 

 mounted beneath a raised cover-slip, into which a drop of Arbacia 

 egg sea-water 1/10 to 1/20 about half-an-hour-old is injected. 

 The naked eye observation shows almost instaneous formation 

 of a ring at the margin of the drop, with simultaneous formation 

 of a clear external zone about 1.5 to 2 mm. wide; the ring then 

 breaks up into small agglutinated masses and so becomes beaded. 

 The trail of substance left in withdrawing the pipette extends to 

 the margin of the cover-slip. It also is a center of attraction and 

 the ring is therefore prolonged by a chain of agglutinated masses 

 to the margin. 



One can observe the details of the reaction best under the micro- 

 scope, using a low power, by bringing the point of the pipette into 

 the field of the microscope and blowing in the drop with the aid of 

 a flexible rubber tube held in the mouth, while looking through the 

 microscope. The reaction takes place so rapidly that it requires 

 repeated observations to observe all the details. In the first 

 second the spermatozoa are aroused to intense activity and form 

 small agglutinated masses within the drop; these then appear 

 actually to 'rush' together (to use the language of my note book) 

 to form larger agglutinations for a period of three to five seconds, 

 after which no more fusion of masses takes place. The aggluti- 

 nated masses thus range from relatively large to relatively small. 

 While this has been going on in the interior of the drop, a ring 



