SEA-FISHERIES LABORATORY. 113 



larva which has failed to find its definitive adult host. 

 It is present in the (modified, no doubt) oncosphere 

 stage in some invertebrate which is eaten both by the 

 Coalfish and by the animal in which the Cestode is 

 sexually mature. Its situation is unusual, but so also is 

 that of T. erinaceus in the body muscles of the Megrim or 

 Halibut, and there, too, the larva is mobile, moving 

 about like a cheese maggot in its cavity ; while it is 

 much larger than the larva of the same species which 

 inhabits the Whiting or Gurnard. The absence of the 

 larval cyst; the growth of a "neck" region; and the 

 direct attachment of the scolex to the tissues of the host, 

 are, however, features not presented by T. erinaceus. 

 The reason that the sexual organs have not developed is 

 doubtless the absence of the specific stimulus to division 

 of the cell rudiments of these organs, afforded by the 

 fluids of the true adult host. 



Lonnberg suggests that his specimen might con- 

 ceivably have been a pathological form, but apparently 

 rejects this possibility. I have no doubt that it is not 

 pathological, and that the only departure from normality 

 is the capacity for an extended period of larval life, and 

 for greater growth than occurs when the regular life 

 history is experienced. 



2. Tetrarhynchus benedeni (Crety).'' 



On July 1st, 1911, a local fisherman, working a 



stake-net at Roosebeck, Morecambe Bay, caught 08 



specimens of the Tope {Gnhor/tiiuis r/o/eus), the fishes 



varying in length from four feet six inches to five feet 



six inches. All were females M'ith well-developed 



ovaries. One of these dogfishes was dissected by my 



* Vaullegeard, A. " Pccherches sur les Tetrarhynques." Mem. 

 Soc. Linn, de Normandie, XJX^ Vol. (ser. 2% Vol. Z") S^fasc. P. 265, 

 PI. XIII. Caen, 1899. 



