200 PROF. HUXLEY ON THE AGAMIC REPRODUCTION 



side, constituting a sort of epithelial layer (c) continuous with the contents of the cham- 

 ber. These, when perfectly unaltered, are constituted by a homogeneous pale periplastic 

 substance (r/), containing about a dozen clear spheroidal cavities (e) whose waUs are 

 a little denser than the rest of the periplast. The cavities have on an average a dia- 

 meter of a^To^th of an inch. In the centre of each is a rounded opake body (/) like 

 one of the eudoplasts of the wall of the dilatation, and, indeed, obviously of the same 

 nature. 



In whatever fluid I have examined this tissue, it began after a time to alter. In the 

 very weak syrup which I ordinarily employed, the change consisted partly in the slightly 

 increased definition of the walls of the clear cavity, but more particularly in the breaking 

 up of the periplast into spheroidal masses, each of which contained a single vesicle and 

 its endoplast*. The resemblance of such a body to an ovum with its germinal vesicle 

 and spot is complete; nor would it be possible for any one ignorant of the origin of 

 the body to say that it was other than an ovum. Water instantly alters the appearance 

 of the tissue, completely destroying its distinctive character. Dilute glycerine shrivels 

 up the vesicles and alters the appearance of their central endoplast, probably by endos- 

 mose. Acetic acid renders the periplast dark, and gives an exceedingly marked definition 

 to the parietes of the vesicle. To see the appearances I have described as normal, the part 

 must be examined perfectly fresh, and in a solution of sugar neither too dilute nor too 

 concentrated. 



In certain specimens the contents of the lower part of the terminal chamber are dif- 

 ferent from those of the upper. As much as a thii'd of the whole chamber may be occu- 

 pied by a mass of periplast containing only a single clear vesicle. Such a condition is 

 figured in fig. 1, PL XXXVI. Fig. 2 exhibits a further advance in the same direction; the 

 mass, which, from its close resemblance to a true ovum, I have called a pseudovum, having 

 enlarged so much as nearly to equal the contents of the terminal chamber, from which it is 

 distinguished by a slight constriction. In figs. 3 and 4, the constriction has become more 

 marked, until at length a penultimate chamber is formed, connected only by a narrow neck 

 with the terminal one, fig. 4. It is on an average about s-guth of an inch in diameter. The 

 epithelial layer (c) of its wall is ordinarily well developed, and when water is added swells 

 up, so as to separate the periplastic substance of the pseudovum from the wall. The peri- 

 plast itself exhibited no structure, and appeared unchanged except in size. The clear 

 vesicle was sometimes unchanged, sometimes enlarged, but otherwise unaltered. Of its 

 endoplast I was sometimes imable to discover any trace ; on other occasions I found a 

 few granules in its place (fig. 3) ; and, once, two particles, each rather more than half its 

 diameter, appeared to lie side by side in the interior of the vesicle. 



The marked contrast between the perfect distinctness of the endoplast in the vesicles 

 contained in the ultimate pseudovarian chamber, and its apparent absence in the very 

 similar vesicle of the mass contained in the penultimate chamber, or in the lower jjart of 

 the last one, was the more striking, as the two could be readily compared under the same 

 circumstances and in the same field of view. 



* Leydig (I. c. p. 63) appears to regard this as the first state of the ovigerms, and he has OTerlooked the 

 epithelium. 



