41s University of California Publications in Zoology. [Vol. fl 



immediately beneath the limiting membrane of the pit. These 

 pits stain an intense blue when the living animal is treated with 

 methylen blue. They take up the stain quickly and hold it for 

 several hours after removal from the staining medium. The 

 function of these pits is totally unknown, but the presence of 

 central nervous tissue immediately beneath their surface indicates 

 their possession of some sensory function. 



E. GENERAL DISCUSSION. 



This investigation was undertaken and carried out in the hope 

 of obtaining evidence which would definitely settle the question 

 of antero-posterior orientation. This evidence was sought along 

 three lines: (1) morphological relationships of organs, in them- 

 selves and compared with other platyhelminths ; (2) behavior of 

 the living animal; (3) embryological history. The writer has 

 unfortunately failed to find any extra-uterine embryological 

 material, and has no evidence from this source to offer. The fact 

 thai Cliim/iini collieic&Ti not be kept in aquaria, even large ones, 

 with any measure of success (Dean, 1906. p. 16) makes the life- 

 history a hard problem to attack. I am convinced that we have 

 thus far no hint whatever as to the intermediate host of Gyro- 

 cotyle. The occurrence of decaying, sexually mature forms in 

 Mactra edulis has. it seems, no bearing on this question. The 

 youngest forms reported, the only immature ones in fact, are the 

 young individuals found by Lonnberg in the spiral valve of ('. 

 monstrosa. This fact indicates that the worm enters the host in 

 a sexually immature condition. The fact that no hatched em- 

 bryos have been found in the intestinal contents of Chimaera 

 indicates that Gyrocolylr, like other cestodes, has at least two 

 hosts. Further than this we know nothing of its life-history. 2 



Conclusive morphological and functional evidence bearing on 

 the question of orientation has been found in abundance. In the 

 course of this work, evidence bearing on certain other questions 



= The discovery by Hungerbiihler (1910) of cysticercoids in the paren- 

 chyma '4' Gyrocotyle rugosa is a recent addition to our knowledge of the 

 embryology of the genus. The embryo resembles the ten-hooked embryo 

 already figured by Spencer as an extra-uterine embryo. Its position (near 

 the uterine pore) suggests that the wall of the uterus may have given way 

 in that region in the preparation of the specimen. 



