MUSEUM OF COMPARATIVE ZOOLOGY. 3 



completely covered with headless stems. As many stones as we could 

 carry were packed in moist paper or in jars, and transported safely 

 several miles. A few days later, stones with living stocks of Urnatella 

 and parts of the barrel-hoop with headless stems were transported in a 

 pail of water to Cambridge. Upon arrival at Cambridge it was found 

 that nearly all the heads had dropped off. The stocks were kept in 

 running water for three months, during which time those which had lost 

 their calyces did not regenerate them; whereas the stocks on the barrel- 

 hoop did regenerate their heads, but did not bud very luxuriantly. 



I cannot close this introduction without expressing thanks to my 

 friend Mr. Potts, who, filled with love for the science, has unselfishly 

 supplied me with material, hospitably received me into his household 

 during my stay in Pennsylvania, and worked with me beyond his 

 strength in our dredging operations on the Schuylkill in order to further 

 a study of this animal. 



The later studies included in this paper were made in the Embryo- 

 logical Laboratory, under the direction of Dr. E. L. Mark. 



I propose to describe first the anatomy of the adult, and, in the second 

 place, the non-sexual reproduction and regeneration, so far as I have 

 been able to determine them. In each section of the paper I shall give 

 first my own observations on Urnatella ; secondly, compare them with 

 those of others on Urnatella or other Endoprocta ; and, finally, give my 

 conclusions upon or interpretation of any difficult points. 



II. Anatomy. 



For the purposes of description we must distinguish the stalk and 

 the calyx. 



1. The Stalk. 

 The stalk is an elongated, filamentous structure, composed of a 

 number of segments, lying one beyond the other. The number of such 

 segments varies from one to several, according to the age of the stalk. 

 Leidy counted as many as eighteen. I have never counted more. 

 Looked at with a hand lens, the stem is seen to be composed of alter- 

 nating translucent and opaqiie rings, of which the former occupy the 

 middle zone of each segment ; the latter have an intersegmental position. 

 The surface of the stalk in the translucent zone is thrown into circular 

 folds, and small processes appear scattered over its surface, more abun- 

 dantly on the more distal segments (Plate I. Fig. 6). 



