DB. T. S. COBBOLD OlS" STRONGTLUS TETRACANTHFS. 291 



equine bearer. If this be so, tlie following conclusions, partly 

 based on analogy, cannot be far from embracing the whole 

 truth : — (1) The eggs are expelled from their parent in a state 

 of fine yolk- cleavage. (2) The embryos are formed after egg- 

 expulsion, and in a few days escape from their envelopes, under- 

 going a primary change of skin in moist earth during warm 

 weather. (3) As rhabditiform Nematoids they enjoy a more or 

 less prolonged existence, probably living many weeks in this 

 state. (4) In all likelihood an intermediary host is unnecessary. 

 (5) The rhabditiform larvse are passively transferred to their 

 equine bearer, either with, cut fresh fodder, or whilst the animals 

 are grazing. (6) Passively transferred to the intestinal canal, 

 they thence enter the walls of the caecum and colon, encyst 

 themselves, and (according to Leuckart) undergo another change 

 of skin. (7) Their presence in the intestinal walls is associated 

 with pathological conditions which frequently prove fatal to the 

 bearer, sometimes creating severe epizooty. (8) Ordinarily the 

 young worms perforate their cysts and immigrate to the lumen 

 of the bowel, where they already afford external indications of sex 

 (Trichonema-stage of growth). (9) They next form cocoons 

 by the agglutination of vegetable debris within the gut, and 

 undergo a third ecdysis attended with intestinal metamorphosis. 

 (10) The formation of the internal sexual organs and the 

 completion of the definitive form is accomplished within the colon 

 of the host. 



The literature of this species is as follows : — 



RuDOLPHi. — (Proles Strongyli armati.) Entozoorum Hist. Nat. vol. i. 



p. 207 (1808-10). 

 Mehlis.^ — (/S. tetracanthus) in Isis, 1831, p. 79 (quoted by Gurlt). 

 GuRLT. — (Vierstacheliger Pallisadenwurm.) Lelirb. d. path. Anat. der 



Haus-saugethiere, Bd. i. p. 355. tab. vi. figs. 23-32 (1831). 

 Knox. — Remarks on the lately discovered Entozoa infesting the 



muscles of the human body ; with some observations on a similar 



animal found beneath the intestinal membrane of the horse. Edinb. 



Med. & Surg. Journ. vol. xlvi. p. 92 (1836). 

 Dick. — (Worms at different stages of growth.) Quoted by Dr. Knox. 

 MiESCHER. — Bericht iib. d. Verhandl. d. nat. Gesellsch. in Basel, 



Bd. iii. p. 5; Ann. d. Sci. Nat. tom. x. p. 191 (1838); and 



Wiegm. Arch. f. Naturg. 1839, 5 Jahrg. Bd. ii. p. 159. 

 DuJARDiN. — {Sclerostoma quadridentatum) Hist. Nat. des Helm. 



1845, p. 258. 

 DiESiNG. — {Sclerostomum tetracanthum) Syst. Helm. vol. ii. p. 305 



[Nematoideum Equi Caballi), p. 332 (1851). 

 Ercolani. — Giorn. d. Vet. 1852, t. i. p. 317 (quoted by Leuckart). 



