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SUMMARY OF CURRENT RESEARCHES RELATING TO 
ticulum of the pineal body. In Lacerta and Anguis it arises from 
the thalamencephalon independent of, though parallel to the epiphysis. 
It is supplied by a transitory nerve not derived from the epiphysis, 
and grows from a parietal centre between the base of the pineal gland 
and the first fold of the choroid plexus. The third eye is an optic 
vesicle evaginated from the thalamencephalon ; the separation between 
crystalline and retinal portion is usually unilateral, rarely bilateral, 
and is late in appearing, therefore not suggestive of a dual origin of 
the eye. Distinct in Cyclostoraata and Reptilia, it is rudimentary in 
Teleostei and Amphibia, absent in Selachii. The epiphysis does not 
represent the stalk of the parietal eye ; it is equally old, constant in 
occurrence, and of entirely unknown function. The paraphysis is a 
diverticulum of the fore-brain, which may give rise to one or more 
secondary vesicles ; it appears in Selachii after the epiphysis and parietal 
eye, and shows no hint of ancestral sensory functions. Of these only 
the parietal eye preserves any trace. 
Vertebrate Ear.* — Mr. H. Ayers devotes the second of his studies 
on “ Vertebrate Cephalogenesis ” to a study of the ear, in which he enters 
upon a number of points which it is not our duty to record here. 
We must content ourselves with stating that he considers the Verte- 
brate ear to be a relatively late acquisition, and that among the Saurop- 
sida and Mammalia it is the only remnant of the canal-organs of their 
ichthyopsid ancestors. He concludes that the surface territory out of 
which the ear developed was the best offered by the anatomical con- 
ditions of the ancestors of present Vertebrates ; the superiority of this 
territory lay in its combining in small space two differently innervated 
sensory apparatuses of a kind suitable for the further perfection of the 
function of the perception of wave motion. Among the higher forms the 
semicircular canals are degenerating, and one canal-organ, the crista 
abortiva, has entirely disappeared. Corti’s organ is not, as Retzius 
concludes, the papilla basilaris, but only a small portion of it, which 
has undergone peculiar modifications. 
The auditory organs of Invertebrates are not the forerunners of 
the Vertebrate auditory organ, but are differentiated structures which 
are strictly confined to them. 
Cleavage of Amphibian Ovum.j — Messrs. E. O. Jordan and A. C. 
Eycleshymer have a preliminary notice of their observations on the 
cleavage of the ovum of various Amphibia. By the use of plane mirrors 
they avoided the necessity of changing the position of the egg. 
Though the first meridional furrow usually divides the egg into two 
subequal portions one cell is sometimes twice as large as the other ; 
so, again, though the second meridional furrow is generally at right 
angles to the first the two may form quite acute angles with one 
auother. The third set of furrows is usually equatorial, but there are 
all possible variations between a true equatorial and a true vertical. 
In the fourth set of furrows each quadrant usually exhibits radical 
individual differences, and if the third set of furrows is irregular the 
fourth is hopelessly intricate. As the embryos formed were quite 
* Journ. of Morphol., vi. (1892) pp. 1-360 (12 pis.). 
f Anat. Anzeig., vii. (1892) pp. 622-4. 
