March 



18S7] 



NATURE 



525 



The time iluring which food granules are thus passing from the 

 follicular cells to the ovum maybe called "the yolk forming 

 period." 



It is succeeded by a period during which the vitelline mem- 

 brane af;ain becomes thin, the follicular cells arc reduced to a 

 single layer, and the cells are very thin and flat. This period 

 may be called the "absorption of fluid period," since during it 

 the ovum absorbs large quantities of fluid through the thin vitel- 

 line membrane and single layer of thin follicular cells, and 

 thereby increases largely in si^e. 



This is in turn succeecle<l by a third period, during which the 

 follicular cells again become active, multiply, increase greatly in 

 size, and give rise between themselves and the vitelline mem- 

 brane to a deeply standing homogeneous layer, which I will call 

 the (horii'it. This period may hence be called "the chorion 

 forming period." All these three periods are gone through while 

 the ovum is still in the follicle. 



Upon the bursting of the follicle and the reception of the 

 ONiim in the Fallopian tube, a few of the follicular cells remain 

 attached to the chorion ; the majority are left behind within the 

 burst follicle. 



During the passage along the Fallopian tube, the vitelline mem- 

 brane again increases in thickness, and the chorion, also increasing 

 in thickness, absorbs fluid and becomes the atbuiiien layer. Out- 

 side this now appears a new structure, ///£■ j/;c// or shell-membrane, 

 of tough parchment-like consistency, • not staining with reagents. 

 I have not yet traced the deposition of the shell to the activity of 

 any special glands ; but I can say that the shell-membrane does 

 not increase at the expense of the chorion or albumen layer. 



.\fter reaching the uterus both vitelline membrane and shell- 

 membrane increase in thickness, but the albumen l.iyer diminishes 

 and disappears, serving apparently for the nutrition of the ovum. 

 Immediately beneath the vitelline membrane a new layer is now 

 seen in hardened preparations ; but it may be shown that this 

 layer is really fluid, yielding a coagulum which stains deeply with 

 reagents, the fluid being apparently derived, through the mem- 

 branes, from the uterine glands. 



In Marsupialia the history of the vitelline membrane, save that 

 " the yolk forming period " is not marked ofl'from the " absorp- 

 tion of fluid " period, is similar to that in Monotremata. I have 

 not been able to trace the beginning of the " chorion " while 

 the ovum is still in the ovary, in Marsupialia ; but in an ovum 

 of Phascolarotos from the uterus, I found a chorion like that of 

 Monotremata, and surrounded moreover by a thin transparent 

 membrane — a shell-membram. Within the uterus the chorion, 

 increasing in thickness, becomes transformed in'o an albumen 

 layer, and is eventually absorbed, passing through the vitelline 

 membrane to nourish the ovum, so that eventually the vitelline 

 membrane comes to be close to the shell. 



Asin Monotremata. a coaiulable, and, when coagulated, deeply 

 staining fluid makes its appearance between the vitelline mem- 

 brane and ovum (blastoderm). 



The shell-membrane persists until the developing ovum 

 becomes fixed to the walls of the uterus, after which it dis- 

 appears. 



The paper then compares the egg-membranes just described 

 with those of Placentalia, and those of Vertebrata generally. 



(2) Scf^'iiienlalion. — The telolecithal ova of Monotremata and 

 Marsupialia go through a partial segmentation. The ova of 

 Placentalia segment completely, but the resulting blastodermic 

 vesicle is identical with that produced by partial segmentation 

 in Monotremata and Marsupialia. 



In Moiiolremala there is a posterior lip to the blastopore 

 similar to that of El.asmobranchii. The epiblast grows in so 

 rapidly from the sides, that a primitive streak region is formed 

 in front of the posterior lip long before the epiblast has 

 inclosed the yolk. This uninclosed area in front of the primitive 

 streak probably includes a region where the hypoblast (yolk) 

 has secondarily broken through the epiblast. The existence of 

 such a region would hide the position of the anterior lip of the 

 blastopore. The circumference of the circle made up by the 

 larger arc of the edge of the blastoderm on the yolk, and the 

 smaller arc of the posterior lip of the blastopore, is a measure 

 cf the quantity of yolk in a meroblastic ovum. 



In Marsii/>ia!ia the epiblastic growth incloses the hypoblast at a 

 very early age, except over a narrow slit in front of the po-torior 

 lip of the blastopore. This slit corresponds to the area inclosed 

 by the circle described above in a meroblastic egg. The primitive 



' In the Kiid egg of Echidna I have not detected calcic salts, but that uf 

 Omithcrhynchus gives rise to ;;as when treated with dilute acid. 



Streak is not conspicuous at an early age because of the large 

 size of the cells. No hypoblast projects through the epiblast in 

 front of the primitive streak region. I would explain the 

 segmentation and the gastrula of Placentalia in the same way. 

 Balfour's objection ("Comp. Embryol.'" vol. ii. p. 187) to Van 

 Beneden's original comparison of the blastopore of the rabbit 

 with that of a frog, is explained away by the presence of a 

 posterior lip to the blastopore in Marsupialia. My explanation 

 postulates the existence of a similar structure in the rabbit. The 

 blastopore of the rabbit corresponds therefore to the whole area 

 marked out by the growing epiblast and the posterior lip of the 

 blastopore, before the closing of the primitive streak region, or 

 to this area minus the secondary extension, caused by the 

 projecting yolk, in Monotremata. 



Linnean Society, March 17. — Mr. \V. Carruthers, F.R.S., 

 President, in the chair. — .\ recommendation of the Council to 

 present to the British Museum, Kew, and the Oxford Botanical 

 Gardens, the Society's carpological collection was submitted to the 

 Fellows, but not approved by them. — Mr. C. B. Clarke, F.K.S., 

 was elected into the Council in the place of Dr. H. Trimen, who 

 resigned. — Mr. A. O. Walker read a paper on the Crustacea of 

 .Singapore. These were collected by Surg.-Major Archer during 

 1879-83. The species were chiefly dredged in 15-20 fathoms, 

 or got on shallow banks. A full list is given of all the forms 

 identified, and several new species are described. Among these 

 are : Doclca telraptera, Xanthc scaberrimiis, H/aii miersii, and 

 Caphyra archcri. — A paper was read by Dr. Geo. King, on 

 the genus Fkiis, with special reference to the Indo-Chinese 

 species. The genus Ficus was founded by Linna;us, and included 

 seven species (" Species Plantarum," ist ed.) Later editions 

 contained 118 species. Blume described 93 Malayan figs, and 

 Ro.xburgh 55 Indian species. In the " Hortus ClifFortianus' ' 

 Linnaeus clearly comprehended the difterence of the sexes, i.e., 

 Caprifig = male, the so-called Fig = female, and Erinosyce = 

 hermaphrodite. 'Vahl seems to h.ave misunderstood the arrange- 

 ment of the sexes, and Blume apparently followed him. Roxburgh 

 is the first writer who exainined minutely the florets of nearly 

 the whole of the species, finding two androgynous and the 

 majority monandrous. Later on Gasparini and Miquel each 

 made a careful study of the flowers of the genus, and separately 

 gave different classifications of the group. Miquel subsequently 

 altered his arrangement, making divisions into six sub-genera, 

 while enumerating 405 Old World, 128 American, and twenty-two 

 species of doubtful nativity. In the "Genera Plantarum" of 

 Bentham and Hooker four of Miquel's sub-genera are admitted, 

 a fifth considered doubtful, and a sixth rejected. These authors 

 regarded Miquel's divisions as too loosely defined, and recom- 

 mended a re-working of the group. Dr. King goes into a 

 lengthened description of the structural peculiarities of the 

 flowers of the genus ficus. He specifies (i) male, (2) pseudo- 

 hermaphrodite, (3I neuter, and (4) female fertile flowers. Besides 

 these, he states that there occurs in all the species of Ficus a set 

 of flowers originally named by himself " inscct-attackcd-feinales" 

 but for which he has adopted Count Solms-Laubach's term ^'gnli- 

 flowers " {Bot. Zeil. 18S5) ; the latter botanist having anticipated 

 him in publication, though King's researches had been com- 

 menced earlier. King enters into the question of these gall- 

 flowers, stating that, in the majority, the pupa of an insect is 

 present, and this pui:a can usually be seen through the coats of 

 the ovary. The pupa when perfected escapes into the cavity of 

 the receptacle by cutting its way through or by bursting these 

 coats ; and fully-developed winged insects are often to be found 

 in considerable numbers in the cavity of the fig. The opening 

 through which each insect has escaped from the ovary in which 

 it has been developed is afterw ards clearly visible. The pupa 

 of the insect must become encysted in the ovary of the gall- 

 flower at a very early period, for about the time at which the 

 imago is escaping from the ovary the pollen of the anthers of 

 the male flower is only beginning to shed. Now, there is nothing 

 in itself remarkable in the mere occurrence in the genus of 

 numerous flowers having the general form of females, which yet 

 by reason of certain peculiarities in their structure are incapable 

 of fertilisation by pollen practically barren ; while at the same 

 time their structural defects fit Ihem for becoming the nidus for 

 the larvae of special insects. But, when the manner in which 

 these malformed female flowers are disposed in the receptacle is 

 inquired into, it becomes clear th.at through the interposition of 

 insects these malformed female flowers may play a most import- 

 ant part in the life-history of many species of the genus Ficus. 

 Thus from the peculiarities in the structure and arrangement of 



