ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 615 



enteron by a wide blastopore, but later on the cavity of that portion 

 of the intestine which grows backwards is closed anteriorly, and in 

 front of this another portion of the embryonic intestine constantly 

 remains in open communication with the exterior ; the anterior fore- 

 gut opens by a crescentic slit, and this would seem to become the 

 mouth of the adult ; in other words, there is no epiblastic stoniodceum ; 

 part of the fore-gat becomes the oesophagus, and the rest appears to 

 be converted into the nephridial system. The nephridia seem to lon<* 

 remain in a more or less embryonic phase, but their history is very 

 difficult to wake out, and is as yet only incompletely known. 



The mesoblast cells, once freely moving about iu the blastocoel, 

 soon accumulate against the inner surface of the plates of secondary 

 epiblast, and the mass increases in size. The process of differentia- 

 tion leads to the appearance of muscle- and nerve- cells at a very early 

 date ; the mesublast cells form a massive group in the prostorniuin, 

 and a comparatively thin cell-sheet in the rest of the body. 



Unexpected as is the mesoblastic origin of the nervous system, 

 , there appears to be no doubt about it; Hubrecht, indeed, thinks that 

 Salensky's figures of Amphyporus vimparus point to the mesoblastic 

 origin of the nervous system in that animal rather than to the mode 

 of origin approved by Salensky. An account is given of the other 

 organs which are developed from the middle germinal layer, and, in 

 conclusion, there are some observations on the differences between an 

 archiccelic and a schizocoelic cavity ; as to the latter term great care 

 must be used in its application, and the extension made by the Hertwigs 

 is unfortunate. An arcluccel is the term to be used when, as with 

 Linens, it is obvious that the cavity has been present from the begin- 

 ning, while that of schizoccel may be reserved for those cases where 

 it can be demonstrated that the perivisceral cavity originates by a 

 process of active scission, and when this scission cannot be looked on 

 as a derivate either of archi- or entero-ccel. 



Filaria terminalis.* — Count N. Passerini describes the anatomy 

 and development of a Nematode found very abundantly in the lun<?s of 

 rabbits, and named by him Filaria terminalis. After discussing the 

 pathological state of the host, he gives a diagnosis of the parasite in 

 the following terms : — the body is cylindrical, filiform, elongated, and 

 transversely striated ; the sexes are separate ; the head has an obtuse 

 form, and is not distinctly separated from the rest of the body ; the 

 terminal, circular mouth is surrounded by six papillae ; the anus lies 

 ventrally and posteriorly, in front of a short, membranous, subconical 

 tail ; the extremity of the male is a little curved forward, and is 

 furnished with a chitinous retractile penis formed of four pieces, of 

 which the two terminal are slighily recurved anteriorly; the sexual 

 aperture of the male lies at the hind cud in a sort of cloaca (in which 

 the intestine also ends), and is surrounded by six soft cirri, of which 

 the first two are bifid at the apex, the two next divided into three, 

 aud the last simple ; there is a single testicle ; the oviparous female 



* Atti ^oc. Ital. tSci. Nat., xxvii. (188A) pp. 12 U3 (5 pla.). 



