148 DESIGN IN NATURE 



At D, the dormant pupa stage has been reached, where the caterpillar has gone into winter quarters within 



ts silent, horny cocoon. . 



The developmental changes are so unUke each other that it is only the expert who can say that we are dealing 



all through with one and the same animal. 



The changes witnessed in so-called development by " alternate generations " are, if possible, more remarkable. 

 Here the development is, as it were, suppressed at a particular period to be commenced at another period subsequently. 



One of the best examples known of development by alternate generations is that furmshed by the obeha, one 

 of the smaller medusae (see Plate xxxv.. Fig. 5, A, B, C, D). • , i i,- r j . 1 



Obeha reproduces itself in two ways : (a) as part of a polype, and (6) as free swimnung buds which detach 

 themselves from the polype and commence an independent existence. It is hard m either case to trace the 

 development of the animal, and for a long time its possible descent by alternate generations was doubted by even 

 advanced naturalists. 



In these cases the offspring in no way resembles the parent. 



The animals which reproduce themselves by alternate generations are generally grouped under zoophytes. 

 They belong to the Hydrozoa, a di^dsion of the Ccelenterata, which also includes the fresh-water polypes, and many 

 jelly-fish, mostly small in size. They are a numerous tribe, and are usually found growing on the rocks and 

 seaweeds of the tidal pools. They resemble dehcate plants rather than animals. Their slender, tapenng, flower- 

 hke stems and branches keep up the delusion. The colonies of polypes vary in size. Thus, in one of the smaUer 

 species {Plumularia cristata) the assemblage varies from 400 to 500 specimens. In some of the larger species (Plumu- 

 laria falcata, or Sertularia argentea), the colony may contain from 80,000 to 100,000 individuals. 



The common tapeworm affords another example of an animal whose developmental changes are interrupted 

 at one point and taken up subsequently at another point. The appearances presented by the various developmental 

 products are, moreover, wholly dissimilar, as a reference to Fig. 34 shows. 



In reproduction by " alternate generations " the product does not in the first instance resemble the original 

 parent or parents. In this form of reproduction, the proofs of design are even stronger than in direct reproduction. 

 Certain parasites, the tapeworm for example (Fig. 34), require more than one host or purveyor for their development. 



This singular creature has a hermaphrodite parent with a nervous system, but no brain proper. It is produced 

 unconsciously, and bhndly launched on the world, but not to perish. It is eaten by a higher animal with other 

 food, and attains its first or cystic stage in the flesh of the unfortunate animal, which involuntarily and unknowingly 

 becomes its host and habitation -pro tempore. Nor does the designed chain of events stop here. The host is in 

 turn eaten, in many cases, by man himself. When the tapeworm reaches the stomach and ahmentary canal of the 

 second host, it is not killed and digested. On the contrary, it pushes its head out of its cyst and everts itself. It 

 ceases to be cystic, and displays a formidable circle of booklets which have been gi-adually forming on the head 

 segment, and with these it securely anchors itself in the mucous hning of the bowel of the second host, imbibes 

 nourishment through its entire substance, and slowly, but surely, becomes an adult tapeworm resembling in all 

 respects its original parent. Neither the tapeworm itself nor its unfortunate hosts display any knowledge of the 

 ultimate object in view. The tapeworm, broadly speaking, is non-intellectual, and the hosts, if intellectual, perform 

 their part of the reproductive process bhndly and involuntarily ; yet the reproduction of a tapeworm cannot 

 be regarded as an accident. On the contrary, the means to ends are complicated and obvious, and bespeak an 

 intelligent power outside the worm and its unconscious hosts. 



What is said of the tapeworm is true of every form of reproduction, even in the higher animals, where there 

 are independent and separate reproductive elements. In the males and females ahke, the reproductive elements 

 make their appearance in the young animals very early, and at a period long antecedent to that of puberty, when 

 they are required. This fact alone proves design. How otherwise is it possible to account for the appearance of 

 structures for which there is no use at the time of their formation ? This fact saps and destroys the argument that 

 organs are formed by use and wont, by habit, by irritabihty, by external stimulation, by environment, &c. In the 

 formation of the reproductive elements none of these causes are at work. The reproductive elements, simple or 

 complex, are original independent entities, and are, in every instance, traceable to their predecessors, whose 

 pecuharities they at once inherit and transmit. 



The spermatozoa or male elements, and the ova or female elements, are not produced by the sexes intelligently ; 

 yet in healthy animals they are formed in anticipation of the time when they will be required. Not only are they 

 not formed intelhgently and voluntarily ; they are formed even in spite of the individuals producing them. Even 

 coitus is not necessarily a part of the reproductive process. 



The conclusion to be drawn from the foregoing is that the production of the sexual elements and even the 

 sexual desire, is not, strictly speaking, under the control of the individuals concerned. The elements and the 



