6 THE AMERICAN MONTHLY [January, 



exhausted vitality in the process of multiplication by division. * * * 

 An impoverished condition is * * * frequently the result of the 

 process of multiplication" (pp. i8, 20). And in an article in the yl:/c>ra^'i'z' 

 for October, 1890, Binet quotes Balbiani (on the subject of fissiparous 

 reproductions among Ciliate infusoria) as saying : " We have established 

 that this mode of propagation has its limits, and ends invariably in one 

 of the three following ways : either by the nattwal and almost simulta- 

 neous death of all the individuals belonging to the same cycle, or by 

 the recurrence of sexual generation leading to the termination of one of 

 the cycles and the commencement of a new cycle, or, finally, to the 

 phenomenon of encystment, which, in fact, brings about only a momen- 

 tary interruption of the process of reproduction by fissiparity." And 

 Binet says : " Miiller had observed that the individuals of any one spe- 

 cies most ordinarily found in coition were, almost all of small stature. 

 Now these individuals of small size * * * are the ones that are the 

 result of a great number of successive bipartitions ; and it is to be ob- 

 served that, in a great many species, in proportion as the bipartitions 

 increase the size of fthe infusoria decreases. « * * Jn Stylonichia 

 pustulata * * * and in all species the body is reduced, and be- 

 comes more and more shrunken, assuming forms and contours very far 

 reinoved from the specif c type. * * * When the vitality of the 

 infusoria has become weakened by a considerable number of agamic 

 reproductions, and the animalcule is upon the point of dying a natural 

 death, a new biological phenomenon can intervene, rejuvenating the 

 animal and rendering it capable of reproducing itself anew for a long 

 series of generations. That phenomenon is fecundation." 



The diatoms, then, follow other well-known examples in both the 

 vegetable and the animal world, passing through cycles of generations 

 by division and by^conjugation. In other words, if the diatoms repro- 

 duce the specific type by means of conjugation so do the desmids and so 

 do the infusoria. The necessity for conjugation therefore in the diatoms, 

 as in the desmids and in the infusoria, arises primarily in my opin- 

 ion from the loss of vitality due to repeated binar}' multiplication, 

 which results in decrease of size of specific type, whether any such pe- 

 culiarity exists as we find in the structure of the diatom or is utterly 

 wanting. There would be fewer examples of the original size in the 

 case of the diatoms if multiplication continued without the repeated 

 intervention of conjugation. But there would always be some exam- 

 ples of the original size, just as many as there were individuals of the 

 species to begin with at the time of multiplication by division, and still 

 more of a size next smaller. Furthermore, T question whether the 

 difference in size between the original frustule and that which is the 

 result of the first division is any greater than is found between the in- 

 dividuals of the same species in repeated instances in the vegetable 

 world without causing any comment.* 



* J. D. Cox has called my attention to his paper on Isthmia. My statement was based on Carpen- 

 ter's representation of Cox's position, viz : that " in Isthmia there are three hoops — two attached to the 

 two valves, and the third overlapping them both at their line of juncture." But I find that Carpenter 

 has misrepresented him. He does not assert that of all cases, only of a part. 



\To be conti?iued.'\ 



