Watson: The Genus Gyrocotyle. 369 



Specimens taken from decaying fish have very generally 

 shown a marked diminution in both lateral frills and terminal 

 rosette. Comparison of these with behavior of fresh specimens 

 kept in culture media shows that the diminution is due to an 

 actual disintegration of tissue. The lateral frills are cut off along 

 a perfectly definite line, running in a slightly irregular antero- 

 posterior course. The line can be made out some twenty-four 

 hours before autotomy actually occurs. In every case where a 

 specimen appears to have no lateral frills or noticeably reduced 

 ones, examination shows a cut edge, along which the frills have 

 dropped off. It is possible that Diesing's original figure was 

 taken from a specimen in which this autotomy had taken place. 

 The frills of the terminal rosette do not appear to be cut off in 

 this regular fashion, but disintegrate on the margins only ; ragged 

 strings of tissue will be found attached to the body of the rosette. 

 Most of the reduction in the size of the rosette in decayed speci- 

 mens I believe to be due to intense contraction of that region, 

 though undoubtedly accompanied by a certain amount of actual 

 disintegration of tissue. When the parasite is left in the dead 

 fish over twelve hours, at ordinary temperature, this decay begins. 



The spines characteristic of this genus are very prominent in 

 G. fimbriata. Their arrangement is in a constant pattern, char- 

 acteristic of this species. This pattern is described in detail 

 later, under the discussion of the cuticula, but its general outline 

 will be given here also for the sake of convenience. In the 

 anterior region, borne on the lateral "fins" above mentioned, are 

 from five to seven rows of very large black spines (pi. 36, figs. 22, 

 23.) They are borne on very low papillae. There are about 

 twenty-five of these spines ; they vary in length, the more anterior 

 and marginal ones being in general the larger. Their form and 

 structure are discussed below, in connection with the description 

 of the cuticula. 



In the posterior region of the body, the spines are longer than 

 those above described. They are borne on large rounded papillae. 

 They form a "collar" (pi'. 34, figs. 10, 12) around the region of 

 the body between the funnel opening of the rosette and the canal 

 opening. On the dorsal surface, no spines are found in front of 

 this collar, which does not extend quite to the level of the canal 



