EUTOZOA. 



143 



The ova of the greater part of the Trcmatoda 

 are excluded prior to the full development of the 

 foetus ; they are generally of an oval but some- 

 times spherical form, and many of <hem singu- 

 larly resemble the seeds or capsules of certain 

 mosses, in having a small circular portion of 

 the outer covering separate from the rest, and 

 closing the cavity of the egg like a lid. 



Nordmann has studied the development of 

 the young of the Distoma hians, which infest 

 the intestines of the perch. According to this 

 excellent observer the foetus raises, in its en- 

 deavours to slip out of the egg, the small lid, 

 and writhes about for some time, being still 

 attached to one point of the egg. In about 

 six hours it succeeds in freeing itself from 

 the egg-coverings; and at this period it differs 

 in every respect from the shape of the parent 

 animal; the body, which is of a mucous con- 

 sistence and perfectly transparent, is of an oval 

 form ; the anterior mouth forms a small square- 

 shaped projection, and the whole surface 

 of the body is beset with many longitudinal 

 rows of short cilia, which are in rapid and 

 incessant motion, and create a vortex in the 

 surrounding water, similar to that which the 

 Polygastric Infusoria produce. The little 

 animal having its anterior extremity diminish- 

 ing to a point, is well formed for swimming, 

 and by means of its vibratile cilia, quickly 

 darts out of the field of vision when under the 

 microscope. At the distance of one-third of 

 the body from the anterior extremity there is 

 a single coloured eye-speck, from which, when 

 pressed between glass plates, there escapes 

 a brilliant blue-coloured pigment. Thus orga- 

 nized, the young of the intestinal parasite just 

 described move to and fro in water as if this 

 were their natural element, and approximate 

 in form and structure most closely to the Poly- 

 gastric Infusoria of the genus Param<ecium, 

 Ehrenb. In this state, doubtless, they are 

 ejected by the Fish, in the intestines of which 

 they were originally developed, into the sur- 

 rounding water, and when again received into the 

 alimentary canal undergo their metamorphosis, 

 lose, like the Lerneae and Cirripedes, the organ 

 of vision which guided the movements of their 

 young and free life, and grow and procreate 

 at the expense of the nutrient secretions with 

 which they are now abundantly provided. 



In the Ctctekmntka the young cast their in- 

 tegument, and would seem in some species, 

 as the Filaria Medinensis, to undergo a change 

 in the form and proportions of the extremities 

 of the body, but they do not possess cilia or 

 ocelli, as in the Trematoda above-mentioned. 



The ova of the Linguatulu are of an oval 

 form : the germinal vesicle is situated near the 

 superficies half-way between the two extremi- 

 ties ; the vitelline membrane is surrounded 

 with a strong cortical membrane : the develop- 

 ment of the foetus takes place out of the body. 

 In the Stnmgyhu g'gas, Strongylus inflerus, 

 and a species of Tric/iosoma infesting the in- 

 testines of the Goatsucker, we have found the 

 foetus completely formed in the ova contained 

 in the uterus or terminal segment of the gene- 

 rative tube, while those in the ovary or narrow 



commencement of the same part were still occu- 

 pied with the granular matter of the vitellus. 



The mature ova of the Strongylus gigax are 

 of an elliptical form, and the embryo within 

 is plainly seen coiled up through the trans- 

 parent coats of the egg; the resemblance which 

 these bear to the Trichina when inclosed in 

 its inner cyst is very striking : the hypothesis 

 suggested by this resemblance need only be 

 alluded to for the purpose of exciting the at- 

 tention of those, who may hereafter meet with 

 the preceding minute muscular parasite, to the 

 existence of larger Nematoid Entozoa in other 

 parts of the body. 



Cloquet describes the ova in the beginning 

 of the ovaries of the Ascaris Lumbricoides as 

 consisting of rounded linear corpuscles, 

 pointed at one extremity, thickened at the 

 other; in the middle of the ovaries they as- 

 sume an elongated triangular form, and one 

 of their angles frequently supports a small 

 spherical eminence; the base of the ovum 

 adheres to the parietes of the oviduct, the apex 

 projects into its cavity. In the enlarged canals, 

 which he terms the cornua of the uterus, the 

 ova are unattached and of a conoid or irre- 

 gularly triangular figure. In the uterus itself 

 they have assumed an ovoid or elliptical form, 

 are surrounded by a transparent glairy mucus, 

 and are composed of a transparent cortical 

 membrane, perfectly smooth on the external 

 surface, and filled with a transparent fluid, in 

 which floats a linear embryo, disposed either 

 in a straight line or coiled up. Cloquet never 

 observed the young Ascarides excluded from 

 the egg in the interior of the uterus, and we 

 equally searched in vain for free embryos in 

 the generative tubes of the Strongylus and 

 Oxyurus above-mentioned, although their de- 

 velopment in regard to form appeared to be 

 complete in the ovum ; the structure of the 

 embryo resembles that of the simpler Vibriones, 

 there being no generative tubes apparent, and 

 the cavity of the body being occupied by a 

 granular parenchyma. 



With respect to the exclusion of the ova 

 in these and similar ovo-viviparous Nematoid 

 Entozoa, it would appear to be very commonly 

 accompanied with a rupture of the parietes 

 of the body and of the generative tube. Ru- 

 dolphi observes, with respect to the Cucullanus, 

 " Ovula, verme quieto, per intervalla ex vulva 

 pullulent ; quin eodem disrupto, quod saepe 

 accidit, ovula vel embryones ex ovariis pro- 

 lapsis parituque ruptis vi quadam et undatim 

 protroduntur." 



The generation of the Filaria Medinemis is 

 of the viviparous kind, and the progeny is 

 countless, " Filariae nostrae," observes Rudol- 

 phi, " prole quasi farctae sunt, quod si harum 

 longitudinem illius vero minutiem spectas, 

 fcetuura multa millium millia singulis tribuit." 

 What is most remarkable is, that these em- 

 bryos are not, as in the Strongylus and the 

 Nematoid genera above-mentioned, enveloped 

 in an egg-covering, nor are they included in a 

 special generative tube, but float freely along 

 with a granular substance in the common mus- 

 cular envelope of the cavity of the body. 



