OVUM. 



[121] 



puscles ; which are held by Nelson thus to pene- 

 trate or gain access to the vitelline substance. 



K. Ovum more advanced ; the vitelline and 

 albuminous membranes formed; clear highly re- 

 fracting spaces resembling altered spermatic cor- 

 puscles are seen in the yolk substance. 



F. Ovum after fecundation; uniform structure 

 of the yolk substance previous to the appearance of 

 the embryonic cell and commencement of segmenta- 

 tion. The chorion has now become tuberculated. 



of the ova appears to consist, first, in the 

 production of minute cell-germs in the upper- 

 most part of the ovarian tube immediately 

 adjoining its coecal termination. It does not 

 appear to be fully ascertained whether these 

 germs are originally, as some have supposed, 

 the maculae or nuclei, or rather, as others hold, 

 the germinal cells or vesicles themselves : the 

 latter opinion appears to be the most probable. 

 Second, the granules of the yolk-substance 

 very soon collect round the exterior of the ger- 

 minal vesicles. These granules appear at first 

 to be suspended in fluid ; but a little later, 

 as they come to collect round the germinal 

 vesicles, they are united together in a mass by 

 a firmer but clear basement substance, and 

 when the minute ova have somewhat in- 

 creased in size, the outline of this clearer 

 basement substance of the yolk is distinguish- 

 able. There is not, however, at first any ex- 

 ternal or vitelline membrane ; of this Dr. 

 Nelson and I have convinced ourselves by re- 

 peated observations in Ascaris mystax.* 



The ova, as they continue to descend in the 

 vitelligenous part of the tube in immense 

 numbers closely pressed together, assume the 

 form of subtriangular flattened bodies, and 

 come to be arranged in series of three, four, or 

 more, in a short spiral round the centre of that 

 part of the ovarian tube which constitutes 

 the yolk organ, as round a central axis, but 

 without being united together by any com- 

 mon stalk or other structure. A prodigious 

 number of ova are thus packed together in a 

 very small space. 



In passing through the next part of tube, 

 which forms an oviduct, the ova are detached 

 from the spiral and closely-set position, and 

 being surrounded by fluid, which must here 

 be secreted within the tube, descend one by 

 one through its narrower part. At this place 

 they encounter the spermatic corpuscles when 

 they are present, and undergo the change of 

 fecundation ; but whether fecundated or not, 

 the ova now lose their germinal vesicles, alter 

 their form from that of flattened triangles to 

 oval, become for a time much more yielding 

 and soft, and somewhat later begin to acquire 

 an external covering which they have not 

 previously possessed. 



The peculiar motionless and tailless sper- 

 matic corpuscles appear, therefore, to come 

 into contact with the ova when the yolk is 

 exposed directly to their action. According 

 to the interesting observations of Dr. Henry 



* See Nelson's paper on the Reproduction of the 

 Ascaris Mystax in the Trans. Roy Soc. of Lond. 

 1852, p. 563., pi. 28, figs. 48. and 50. 



Development of Spermatic Corpuscles in Ascaris 

 mystax. 



This figure is introduced to show the several 

 stages of development of the peculiar acaudal and 

 motionless spermatic corpuscles of the Ascaris 

 mystax. 



A. shows various stages of the primary sperm - 

 cells or rather sperm-germs; in the more advanced 

 of which towards the right, internal cells are seen 

 forming by endogenous production within the 

 primary germ-cells. 



B. & c. show the second stage, in which the sepa- 

 rated germ-cells have each become covered by a 

 finely granular mass collected round them ; in B. 

 this process is beginning ; in c. it is completed, and 

 the sperm cells thus formed have assumed an ovoid 

 shape. 



D. Two views of sperm-cells in the third stage, in 

 which a quadrifid division of the whole cell has 

 taken place preparatory to the escape or separation 

 of the spermatozoon-cells, usually four in number, 

 proceeding from each sperm-cell. 



E. Various views of these spermatozoon cells in 

 which the radiated linear marking (seen in D.) has 

 disappeared, and is again resolved into granules ; 

 the nucleus is seen from above in the left-hand 

 figure ; in the three others being viewed in profile 

 the appearance of the bell-shaped spermatic cor- 

 puscle with the nucleolus is perceptible. 



F. Exhibits from right to left the various pro- 

 gressive stages of the bell-shaped corpuscle into the 

 test tube form ; the remains of the nucleolus and 

 granular substance are seen towards the mouth of 

 the flask-shaped bodies. 



o. Illustrates the effect of water in developing 

 " Sarcode " on the exterior of these corpuscles in 

 two different stages of their advancement. 



