PfiOSTHECOSAOTEB. 91 



Fourthly. The plan I have here adopted by way of experiment. 

 This method is evidently only necessary when the disease has so 

 far advanced that immediate suffocation becomes inevitable ; or it 

 may be resorted to when other methods have failed. In the most 

 far-gone cases instant relief will follow this operation, since the 

 trachea may with certainty be cleared of all obstructions. 



Lastly. Perhaps the most essential thing to be observed, in 

 view of putting a check upon the future prevalence of the disease, 

 i^ the total destruction of the parasites after their removal — a pre- 

 caution, however, which cannot be adopted if Mr. Montagu's mode 

 of treatment is followed. If the worms be merely killed and 

 thrown away (say, upon the ground), it is scarcely likely that the 

 mature eggs will have sustained any injury. Decomposition 

 having set in, the young embryos will sooner or later escape from 

 their shells, migrate in the soil or elsewhere, and ultimately find 

 their way into the air-passages of certain birds in the same 

 manner as their parents did before them.* 



Prosthecosacter. — Three well-defined species of this curious 

 genus are known to infest the common porpoise, whilst a fourth 

 has been found in the narwhale. The three forms first mentioned 

 (Prosthecosacter inflexus, P. convolutus, and P. minor) are readily 

 distinguishable from each other by their relative size and length, 

 and also more especially by the form of their caudal extremities. 

 The females of P. inflexus are capable of attaining a length of nine 

 inches, those of P. convolutus may be upwards of an inch and a 

 half in length, whilst those of P. minor have not hitherto been 

 known to exceed the inch. The species described by Leuckart, 

 from the narwhale (P. alatus), is only half an inch long. All the 

 forms from the porpoise were met with by Professor Quekett ; two 

 of the species have been noticed by myself, and one of them has 



* The foregoing remarks form part of a communication published in the Linnean 

 Society's Proceedings for 1861. The paper was also reprinted in " The Field" of June 

 22nd in the same year, Vol. xvii., No. 443, p. 560 ; and likewise in the " Edinburgh 

 Yeterinary Review," Vol. iii., p. 439, 1861 . 



