BIOLOGY, MARINE — MAYER. 115 



minute details of structure. Professor Conklin's discovery is one 

 of wide-reaching import, and it is but fitting that his masterly re- 

 searches of the past years should thus have led him to the revelation 

 of a fundamental law of zoology. 



Preliminary Report of B. G. Conklin upon the Structure of the Egg 



of Liner ges, etc. 



I joined the yacht Physalia at Key West on April 21, and during my stay 

 on the yacht and at the Carnegie station at Tortugas, from April 22 to May 

 13, 1905. I made, in addition to many general observations on the rich and 

 varied fauna of that region, detailed observations on the early development 

 of a scyphomedusa, Lincrges mercurius, and a study of two remarkable ac- 

 tinian larvae which are quite unlike any other larvae ever yet described. 



In Linerges the cleavage of the egg is total and regular and a typical in- 

 vaginate gastrula is formed which, by closure of the blastopore and elonga- 

 tion of the larvae, gives rise to the usual planula. The polarity of the egg 

 bears a definite relation to the polarity of the larvae, the animal pole of 

 the former corresponding to the apical pole of the latter. Furthermore, the 

 substance of the egg is differentiated into at least three concentric layers, 

 which are recognizable at every stage from the unsegmented egg to the planula. 

 These layers correspond in a general way to the ectoderm, mesoderm, and 

 endoderm of the larva.' Owing to the sudden disappearance of these jelly- 

 fish I was unable to test experimentally the potency of these different layers 

 of the egg. It seems probable, however, that the observed totipotence of 

 fragments of Medusa eggs (Maas, Zoja) is due not to the lack of differentia- 

 tion in the egg substance but rather to the concentric localization of such 

 different substances as are visible in Linerges. 



The two types of actinian larvae which I studied are each characterized by 

 the possession of a membranella, or locomotor organ, composed of fused 

 cilia. In one type this membranella is circular in form, surrounding the body 

 about one-third of the distance from the oral to the aboral pole. In the other 

 type the membranella is longitudinal, running along the ventral side from the 

 oral pole two-thirds of the way to the aboral pole. These larvae have the 

 mesenteries well formed, but show no trace of tentacles. 



Dr. R. P. Cowles carried out an elaborate series of studies upon the 

 reactions and behavior of a number of species of Ophiurans and of 

 the ghost crab, Ocypoda arenaria. Dr. Cowles presents the follow- 

 ing preliminary report : 



Preliminry Report of R. P. Cozvles upon the Behavior of Ocypoda 



arenaria. 



Ocypoda arenaria, commonly known as the sand crab or ghost crab, is 

 found in great abundance on Loggerhead Key, and its burrows occur generally 

 along a belt extending from the shore-line to 20 or 30 feet from it. These 

 usually consist of a main passage opening to the exterior and extending down 

 into the sand at an angle of about 45 degrees, with a more or less vertical 



