Spiritualists have, as a rule, sought to convince not by testimony but by ocular demonstration.
One of these is the ocular segment, in front of the antennal, and behind the primitive preoral segment.
Or " vertex," the compound eyes and the front divisions of the genae are formed by the cephalic lobes of the embryo (belonging membrane analogous to the amnion of higher Vertebrates andto the ocular segment), while the mandibular and maxillary segments known by the same term.
But the protocerebrum contains the ganglia of the ocular segment in addition to those of the procephalic lobes.
I, Ocular segment.
These will then remain as typically composed each of six appendage-bearing somites - the prosoma comprising in addition the ocular prosthomere.'
It seems that confusion and trouble will be best avoided by abstaining from the introduction of the non-evident somites, the ocular and the praegenital, into the numerical nomenclature of the component somites of the three great body regions.
We shall, therefore, ignoring the ocular somite, speak of the first, second, third, fourth, fifth and sixth legbearing somites of the prosoma, and indicate the appendages by the Roman numerals, I, II, III, IV, V, VI, and whilst ignoring the praegenital somite we shall speak of the first, second, third, &c., somite of the mesosoma or opisthosoma (united mesosoma and metasoma) and indicate them by the Arabic numerals.
Limulus thus agrees with Scorpio and differs from the Crustacea, in which there are three prosthomeres - one ocular and two carrying palpiform appendages.
A somite placed between the prosoma and mesosoma - the prae-genital somite - appears to have belonged originally to the prosomatic series (which with its ocular prosthomere and palpi FIG.
O, Ocular tubercle.
If a telescope be employed there is a distinction to be observed, according as the half-covered aperture is between the eye and the ocular, or in front of the object-glass.
A, Anterior ocular or orbital, or praeorbital or anteocular.
Again, in an ocular heliometer by Steinheil double image is similarly produced by a divided prism of total reflection placed in parallel rays.
He endeavoured to illustrate the subject by a clavecin oculaire, or ocular harpsichord; but the treatise and the illustration were quickly forgotten.
By suitably replacing the ocular of the observing telescope in an angular vision spectroscope by a photographic camera, it is possible to photograph spectra; such instruments are termed spectrographs.
The intra-ocular tension is markedly lowered.
It is used in all cases where one needs to reduce the intra-ocular tension, and for this and other reasons in glaucoma.
Again, no single point in the cortex evokes the act of ocular convergence and fixation.
The sight of many an eye has been destroyed by the use of atropine - in ignorance of this action on the intra-ocular tension - in cases of incipient glaucoma.
The use of atropine is absolutely contra-indicated in any case where the intra-ocular tension already is, or threatens to become, unduly high.
The fourth ocular result of administering atropine is the production of a slight but definite degree of local anaesthesia of the eyeball.
The drug is often replaced in ophthalmology by homatropine - an alkaloid prepared from tropine - which acts similarly to atropine but has the advantage of allowing the ocular changes to pass away in a much shorter time.
An ocular segment claimed by the former division is not present or in no case demonstrable in the latter.
Here the articulation of the ocular segment is unusually distinct, and here two characters quite foreign to all the preceding groups come into view.
Usually the sides of the carapace are strangely produced into a mock rostrum in front of the ocular lobe, be it oculiferous or not.
Occasionally the ocular lobes are articulated.
During the paroxysms, or even preceding them, certain sensory disturbances may be experienced, more especially affections of vision, such as ocular spectra, hemiopia, diplopia, &c. Gout, eyestrain and intestinal toxaemia have been put forward as causes of migraine, and Sir W.
Apart from the possible existence of an ocular ep FIG.3.
In the main, the various types of minute ocular structure correspond very closely to the different groups into which mammals are divided, this correspondence affording important testimony in the favour of the general correctness of the classification.