STUDIES ON ASPLANCHNIA EBBESBORNII. 2O3 



however, is comparable to the conditions found in the female 

 (A, n). The cells from which the oesophagus, stomach and 

 digestive glands are formed in the female, become independent 

 of the pharyngeal wall in the male (C, 12-13), and persist more 

 as a compact mass of cells, entirely free from any lumen (C, 

 14-15). The position of these cells within the body cavity is 

 indicated in figures C, 11-15. This group of cells gradually 

 becomes smaller and takes up a final position in the dorso- 

 posterior region of the body cavity, where they are held in posi- 

 tion by delicate muscle fibers. In extreme cases, when the male 

 lives longer than normal, the cells completely disappear within 

 the body cavity and no doubt serve as food. The reproductive 

 organs are well developed (C, 11-15) ar >d communicate with the 

 urinogenital sinus by means of the vas deferens (C, 14). The 

 urinogenital sinus is ciliated, which aids in the passage of the 

 sperm. No attempt was made to represent more than a few 

 of the muscle fibers within the body cavity. The excretory 

 system which is well developed in the male is not shown. 



The development of the digestive system reaches its greatest 

 differentiation in the female as represented in series A. The 

 stomach becomes a rather large strongly ciliated pouch, and 

 communicates with the pharynx by means of a slender oesopha- 

 gus, which is capable of considerable distention (A, 12-13). 

 The stomach ends blindly. There is no indication of a rudi- 

 mentary intestine in the developing embryo. The bladder (con- 

 tractile vacuole) is formed by an a'nterior evagination of the wall 

 of the urinogenital sinus. 



ACTIVITIES OF THE MALE. 



Varying degrees of degeneration are found in the males of 

 Asplanchnia ebbesbornii, ranging from those without a functional 

 digestive system , to those with all organs wanting except a large 

 testis and the delicate hypodermis. The latter is little more than 

 a sperm sac. In both instances however, the sperm are functional 

 and capable of fertilizing the resting eggs. The methods of 

 fertilization are rather unique. The normal free-swimming male 

 is sexually mature at birth, and true intromission occurs at the 

 urinogenital sinus (cloaca) with either kind of female. In the 



