39^ 



DESIGN IN NATURE 



(at or about the monthly periods) the structures which confine them on the surface of the ovaries. The original 

 production of the immature eggs, their ripening, and discharge from the ovaries cannot, even by a stretch of the 

 imagination, be regarded as due to inherent irritabihty or stimulation of any kind, and still less to environment 

 (Plate xci.. Fig. 3, page 393). 



The eggs are discharged for the most part singly or in pairs by an accumulation of serous fluid, it occasionally 

 happening that three and even four or more eggs are Hberated : a multiplicity of eggs meaning, as a rule, a multi- 

 plicity of offspring. The egg or eggs liberated from the surfaces of the ovaries tend to, and occasionally do, fall into 

 the abdominal cavity, in which case the dangerous condition known as extra-uterine pregnancy occurs. In order to 

 prevent such a catastrophe, nature, ever watchful, provides two special tubes called the Fallopian tubes to conduct 

 them to the interior of the uterus. These tubes are very remarkable structures, and are armed with very ample 

 powers. They spring from the horns of the uterus, and terminate in free, funnel-shaped, fimbriated extremities ; their 

 function being to seize the mature egg or eggs and transmit them to the interior of the uterus (Plate xc. 

 Fig. 7, page 391). 



The manner in which they do this is of transcending interest, and affords one of the best-known examples of 

 co-ordinated, vital action. It also affords a striking instance of design. The free, fimbriated extremities of the 

 Fallopian tubes Uterally search for and find the ripe egg or eggs on the surface of the ovaries. These they seize as 

 if with hands, and slowly transmit along their interior (largely by ciHary action), coating them in transitu with a 

 layer of albimien which at once affords them nourishment and faciUtates their progress. The Fallopian tubes exercise 

 similar functions to those discharged by the oviduct of the bird already described. They perform their movements 

 and provide their peculiar secretion quite apart from irritation or stimulation, as supposed. The egg or eggs, when 

 once fairly lodged in the Fallopian tubes, are in the best possible position for impregnation, and here impregnation 

 generally takes place. As already explained, it happens occasionally that gestation occurs in the tubes, and when 

 it does, the abnormal and critical condition known as Fallopian tube pregnancy is established. At rare intervals 

 the impregnated ovum escapes into the abdominal cavity. Abdominal and Fallopian tube pregnancies are, fortu- 

 nately, exceedingly rare events. The world-renowned Csesar was the product of an abdominal pregnancy, and gave 

 his name to the formidable obstetric operation known as the " Caesarian section." 



The spermatozoids, ova, uterus, &c., are figured at Plate xci., page 393. 



PLATE XCI 



Plate xci. illustrates the developments of the brain : it also shows various kinds of spermatozoa, an ovum and 

 ovary, and a human uterus (natural size). 



Fig. 1. — A. A nerve tube with opening at either end. 



B. Expansion and bulging of brain substance at anterior end of nerve tube. 



0. Expansion and division of nerve tube into three primary vesicles : I. forebrain ; II. midbrain ; III. hindbrain. 



D. Further expansion and subdivision into five primary vesicles, a, Cerebrum ; h, thalamencephalon ; c, optic lobes ; d, cere- 

 bellum ; e, medulla oblongata. The primary nerve tube is now known as spinal cord (/). 



E. Further expansion and differentiation, a, Cerebrum ; b, pineal body ; i , optic lobs ; rf, cerebellum ; e, medulla oblongata ; 

 /, spinal cord ; g, olfactory lobe ; h, pituitary body ; i, notochord (after Huxley). 



Fig. 2. — Spiral spermatozoa of various kinds. 



A. Spermatozoon qI Iviton (Triton cristatus), x 450. 



B. Spermatozoa of rabbit {Lepus cuniculus), x 450. 



C. Spermatozoon of field mouse {Arvicola arvalis), x 450. 



D. Spermatozoon of wood shrike (Litnius riifits), x 450. 



E. Spermatozoon of gold finch (Frinyilla elegans), x 450. 



F. Spermatozoon of Perca (Pena/MOT'aii'fe), x 450. 



G. Spermatozoon of blackbird ( Turdus merula), x 450. 

 H. Spermatozoon of man (Homo sapitns), x 450. 



1. Spermatozoon of frog (liana temporarm), x 450. 

 J. Spermatozoon of rat [Mus raftus), x 450. 



K. Spermatic cyst of common creeper bird (Certhia fainilinris), containing a bundle of spermatozoa, x 500. 



L. Spermatic cyst of rabbit. ((, The globules, each of which contains a spermatozoon, x 350 ; h, separate globuli x 500 (after 

 Griffith and Henfrey). ' 



Fig. 3. — Portion of human ovary with mature and immature ova. u, Mature follicle and ovum, consisting of membrana granu- 

 losa, zona pellucida, vitellus, germinal vesicle, and germinal spot ; h, epithelium ; v, stroma ; d, immature ova ; e, immature follicle 

 (after Fothergill). 



