REPRODUCTION IN PLANTS AND ANIMALS. 



REPRODUCTION IN PLANTS AND ANIMALS. 



substances act tike water, however much they may be concentrated, 

 uch M solution* of gum arable, vegetable mucus (gum tragaoanth, 

 mucilage of quince-weds), an-l of dextrin. Concentrated solutions of 

 other substances, in thU owe also, reatore the motions. 



7. Many organic substance* C*UM the motion* of the filament* to 

 ran, owing to their chemical action upon them, such ai alcohol, 

 crrasole, tannin, and ether ; other* owing to their mechanical effects, 

 a* most oil*. Narcotic*, in certain degrees of concentration, are not 

 injurious. 



8. Metallic tall* are injurious, even in extremely dilute solutions ; 

 tuch, for instance, a* a solution containing l-10,000tb of corrosive 

 lublimate. 



9. Most of the alkaline and rarthy salt* are innocuous in certain 

 Jsmriiii* of concentration, which in some is greater and in some Irs* ; 

 so little hurtful, in fact, are they, that the filament* may be kept alive 

 in thorn for from one to four hours. Among these msy be enumerated 

 solution* of common salt ; chloride cf potassium; sal ammoniac; 

 nitrate of soda; nitrate of potass, containing 1 part to 100; more- 

 over, solution* containing from 5 to 10 part* in 100 of phosphate of 

 soda ; sulphate of soda ; sulphate of magnesia ; chloride of barium. 

 As regards some of these salt*, the fact had been previously noticed 

 by older writer*, and more recently by Quatrefages, Newport, and 

 Ankermaun. Solutions unduly diluted have the same effect as water, 

 and cause the formation of loops, but the filaments are revived upon 

 the addition of a concentrated solution of the same salts and of 

 indifferent substances (sugar, urea, &c.). Stronger saline solutions 

 than are required, also interfere with the motions ; but, in this case 

 likewise, the filament* are capable of revival upon the addition of 

 water. These salt* can scarcely be regarded properly as revivifiers, 

 a* was asserted not long since by Moleschott and Ricchctti, for 

 filament* which have become quiescent in indifferent substances, 

 a* sugar, for instance, are not revivified again by them ; and their 

 action is widely different from that of the real excitant* the 

 caustic alkalies. It cannot be denied that their influence is very 

 favourable, and that (but perhaps owing only to their rapid diffusion 

 in the water) they produce motion in a seminal mass more rapidly 

 than other less diffusible substances, such as sugar and albumen ; on 

 which account the above-named authors ascribe revivifying pro- 

 perties to them a fact which, before them, had been made known, as 

 regards common salt, by Quatrefages, and by Newport, for carbonate 

 of *oda and potass; which Utter salt*, moreover, in certain experi- 

 ments, caused the motion to cease in 10' or 16', almost like the caustic 



10. Acids, even in very small quantity, are injurious; such as 

 hydrochloric acid, in the proportion of 1-7, 500th. 



11. Caustic alkalies (soda, potass and ammonia, not lime and 

 barytea), in all degree* of concentration, from l-31th to 6-10th are 

 special excitant* of the spermatic filaments. Whether the latter have 

 become quiescent spontaneously, as in old sperm-fluid, or have ceased 

 to move in indifferent solutions, the above substances recal the most 

 active movement* which are not distinguishable from the vital. But 

 then motion* cease after two or three minutes, and from this qui- 

 escence the filament* cannot be roused by any means. When mixed 

 with indifferent substance* in small proportions (from 1-1 000th to 

 1-iOOth), as, for instance, in syrup, the caustic alkalies afford a means 

 by which the motion* of the spermatic filaments may be maintained 

 for a long time. 



1 'L The sperm-fluid dried in indifferent substances, and in saline 

 solution*, may, in certain cases, have it* motion restored by dilution 

 with the same fluid, or with water. 



The cells which give origin to the spermatic filaments are found 

 upon the surface of the organs which secret* them. At first they are 

 not to be distinguished from ordinary epithelial cells, but they increase 

 in rite, and at last present a corpuscle (seminal corpuscle) in their 

 interior. Then corpuscles are filled with granular matter, which is 

 gradually converted into the spermatic filament, which is at first 

 coiled up, and lie* in contact with the inner surface of the wall of 

 the corpuscle. The spermatic filament* usually present themselves 

 in clusters, which arise* from their tendency when set free from their 

 0*11* to arrange themselves in this manner. 



The six* of tb* spermatic filament* varies. In human beings they 

 are from 1 -&00th to 1 -600th of an inch in length. The head is about 

 1-tOOOth to 1-bOOOth of an inch long, and is about half a* wide. 



In the females of most animals it is not difficult to find a large cell, 

 which is called an ovum or egg. If this ovum be examined in the 

 Mammal*, it will be found to present a vesicle, which is called the 

 germinal vesicle, and this vesicle present* a spot, called the germinal 

 pot There seems to be little doubt that this vesicle is truly the 

 (ra-ctll. In the Ummmalia the ova ire found in an organ called the 

 ovary. 



" If the structure snd formation of the human ovary be eiamin< d 

 at any period between early infancy and advanced age, but especially 

 during that period of life iu which the power of conception exists, it 

 will be found to contain, on an average, from fifteen to twenty small 

 veaicl** or membranous sacs of various sins; then have been already 

 alluded to as th* follicles or vesicle, of I)e Uraaf, the anatomist who 

 first accurately described them. At their first formation, the Onafian 

 vsmicles are small, and deeply seated in the substance of the ovary ; 



but as they increase in tin, they make their way towards the surface ; 

 and when mature they form little prominences on the exterior of the 

 ovary, covered only by the peritoneum. Each follicle is formed with 

 an external membranous envelope composed of fine nbro-cellular 

 tissue, and connected with the surrounding stroma of the ovary by 

 networks of blood-veiuela. This envelope or tunic is lined with a 

 Inyer of nucleated cells, forming a kind of epithelium or internal tunic, 

 and named membrana granulosa. The cavity of the follicle is filled 

 with an albuminous fluid, in which microscopic granules float ; and 

 it contains also the ovum or ovule. The ovum is a minute spherical 

 body situated, in immature follicles, near their centre ; but iu those 

 nearer maturity, in contact with the membraua granulosa, at that 

 part of the follicle which forms a prominence on the surface of the 

 ovary. The cells of the membrana granuloaa are at that point more 

 numerous than elsewhere, and are heaped around the ovum, forming 

 a kind of granular zone, the discus proligerus. 



" In order to examine an ovum, one of the Qraafian vesicles, it 

 matters not whether it be of small size or arrived at maturity, should 

 be pricked, and the contained fluid received upon a piece of glaav 

 The ovum then, being found iu the midst of the fluid by means of a 

 simple lens, may be further examined with higher microscopic powers. 

 Owing to its globular form, however, its structure cannot be seen 

 until it is subjected to gentle pressure. 



"The human ovum is extremely small, measuring, according to 

 Bischoff, from l-240th to l-120th of an inch. It* external investment 

 is a transparent membrane, about l-2500th of an inch in thickness, 

 which, under the microscope, appears as a bright ring, bounded exter- 

 nally and internally by a dark outline : it is called the zona pellucida 

 or vitelliue membrane, and corresponds with the chorion of the 

 impregnated ovum. It adheres externally to the heap of cells consti- 

 tuting the discus proligerus. 



" Within this transparent investment, or zona pellucida, and usually 

 in close contact with it, Us the yelk, or vitellus, which is composed 

 of granules and globules of various size?, imbedded in a more or less 

 fluid substance. The smaller granules, which are the more numerous, 

 resemble in their appearance, as well as their constant motion, pigment 

 granule?. The larger granules, or globules, which have the aspect of 

 fat globules, are in greatest number at the periphery of the yelk. The 

 number of the granules is, according to Bischoff, greatest in the ova 

 of carnivorous animals. In the human ovum their quantity is 

 comparatively small. 



" The substance that combines the globules and granules of the yelk 

 is in many animals quite fluid. The yelk then completely fills the 

 cavity of the zona pellucida, and escapes in a liquid form when that 

 membrane is ruptured : but in ova of the human subject, and some 

 animals, the yelk is much more consistent, and sometimes escapes a* 

 a solid globular moss when the zona pellucida is torn. It is, according 

 to Bischoff, solely owing to this firm consistence of the yelk that it in 

 many cases preserves its form when a watery fluid passes by imbibition 

 through the zona pellucida, and that an interval is theu ap[>arent 

 between the yelk and that membrane. From the appearances resulting 

 from the action of water on the ovum, and from other circumstances, 

 it has been thought that the mass composing the yelk is surrounded 

 by another membrane within the zoua pellucida, but the evidence for 

 such a view is not satisfactory. 



" In the substance of the yelk is imbedded the germinal vesicle, or 

 vesicula germinativa, ThU vesicle is of greatest relative size in the 

 smallest ova, nnd is in them surrounded closely by the yelk, nearly iu 

 the centra of which it lies. During the development of the ovum the 

 germinal vesicle increases in size much less rapidly than the yelk, and 

 come* to be placed nearer to its surface. In a mature ovum of the 

 rabbit it is about one-sixtieth of a line in diameter (Bischoff) : its size 

 in the human ovum has not yet been ascertained, owing to the diffi- 

 culty of isolating it It consist* of a fine transparent structureless 

 membrane, containing a clear watery fluid, in which are sometime* a 

 few granules. 



' At that part of the periphery of the germinal vesicle which is 

 nearest to the periphery of the yelk is situated the germinal spot, a 

 finely-granulated substance, of a yellowish colour, strongly refracting 

 the rays of light, and measuring, in the Mammalia generally, from 

 1 -3600th to l-2400th of an inch (Wugner)." (Kirkes and Pnget, 

 ' Handbook of Physiology.') 



The act of fecundation is effected in the same manner in animals as 

 in plants, that is, by the contact of the sperm-cells with the germ-culls. 

 Much discussion ha* taken place a* to how this occurs, but the follow- 

 ing account may be regarded a* embracing the fact* most generally 

 accepted : As the germinal vesicle becomes fitted for fecundation, it 

 loses its pellucid character, arising from the development of a large 

 number of cells in its interior. It is at this period that the spermatic 

 filament*, coming iu contact with it, produce that tendency to growth 

 which results in the formation of the new being. The nature of this 

 contact has been a question. Mr. Newport however, in a series of 

 very carefully-conducted experiments upon the Amphibia, comes to 

 the conclusion that the spermatic filament penetrates the vitellina 

 membrane, and comes directly in contact with the germinal vesicle. 

 There is no special foramen for the admission of the spermatic fila- 

 ment*, but they pierce through this membrane, and may be seen 

 floating about in the yelk. Mr. Newport found that a single eperma- 



