Cluster formation of spermatozoa 127 



can be produced if we add 2 or 3 cc. of -^ NaOH to 50 cc. of sea 

 water.'' He found recently a good method of producing sperm 

 agglutination with less alkali in the case of the sperm of starfish. 

 When this sperm is put into 50 cc. sea water + 0.5 cc. ^^ NaOH it 

 shows a tendency to agglutinate only after about one hour. But 

 we can produce a real agglutination of the spermatozoa after 

 about only twenty minutes when we put the sperm into the super- 

 natant sea water of eggs or sperm of purpuratus. This agglutina- 

 tion is not specific, since it can also be produced by a great many 

 other substances, e.g., cattle serum or even white of egg. In this 

 case the spermatozoa at first stick together to form sjiort rows or 

 threads; and later the threads begin to ^tick together and form 

 irregular networks. At no time is there any appearance of clus- 

 ter formation or anything suggesting the phenomena of surface 

 tension. 



The writer is therefore under the impression that the cluster 

 formation of the sperm in the supernatant sea water of its own eggs 

 is a phenomenon of a different type from agglutination. 



MOTILITY OF SPERM AND CLUSTER FORMATION 



In observing the clusters the writer was struck with the fact 

 that the spermatozoa at the periphery of a cluster are in free pro- 

 gressive motion, a fact which is incompatible with the assumption 

 of agglutination. When the clusters were small or when the sperm 

 suspension was thin it was possible t,o observe the spermatozoa 

 which are in the center of the cluster. It was seen that the sper- 

 matozoa in the center also were in very lively motion, with the pos- 

 sible exception of small lumps or groups of spermatozoa which 

 may have stuck together. The clusters reminded the writer of a 

 dense swarm of insects which move like a coherent mass through 

 space. These clusters move like one solid body through the 

 water, notwithstanding the fact that the individual spermatozoa 

 are free to scatter. 



Under the influence of these observations the writer formed the 

 idea that the cluster formation and possibly the apparent phenom- 

 ena of surface tension might be the outcome of some tropistic 



3 Loeb, Arch. f. d. ges. Physiol., Bd. 99, p. 323, 1903; Bd. 104, p. 325, 1904. 



