ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 781 



pose." The autbor tlien refers to the recently published observations 

 of Nussbaum and Gruber, to which reference has already been made 

 in this Journal.* 



2. Duplication of parts. The evidence on this head is to be 

 judged under the considerations that instances are by no means un- 

 usual, and that the agreement with the normal structure is not uni- 

 form. 



3. Asexual reproduction. There may be fission or gemmation, or, 

 as an extreme, multiplication by means of pseudova. 



" The evidence forces us to the conclusion that the formative 

 force or cause is not merely the original disposition of the forces and 

 substance of the ovum, but that to each portion of the organism is 

 given (1) the pattern of the whole organism ; (2) the partial or com- 

 plete power to reproduce the pattern." In other words, the formative 

 force is a diffused tendency, and the very vagueness of the expression 

 is useful as emphasizing our ignorance of its real nature. 



Dr. Minot insists on our total or comparative ignorance of the 

 fundamental properties of life, the assertions concerning which are, 

 for the most part, entirely worthless. 



Tail of Human Embryo. f — Prof. H. Fol discusses the question 

 whether the human embryo ever presents at the posterior extremity 

 of its body anything which merits the name of tail. It is necessary at 

 the outset to distinguish teratological cases from the more important 

 phenomena of normal embryogeny, and to agree as to the meaning of 

 the word tail. Is this term applicable to every conical or cylindro- 

 conical appendage at the posterior extremity of the back, whatever 

 may be the tissues of which it is composed, or should it be reserved 

 for an organ containing a prolongation of the vertebral column? 

 This latter definition seems to preponderate. An appendage devoid 

 of vertebras is not a true tail in the anatomical sense of the term, 

 but merely a simple caudal prolongation. 



As regards young embryos, an understanding is not possible if we 

 do not first determine the point where the caudal vertebras begin. 

 Shall we fix the limit at the point where the tail branches ofi" from 

 the body ? Or are we to be guided by the position of the anus ? Or 

 must we give the name caudal to all the vertebrte situate behind the 

 sacrum ? This last-mentioned view has prevailed in comparative 

 anatomy, and from this point of view wo may say that the adult man 

 possesses a tail, since he presents four or five coccygeal vertebrae, 

 situate beyond the sacrum. The minimum in this respect is reached 

 hy the chimpanzee, which has only two or three coccygeal vertebra). 

 This ape is consequently, when mature, further from possessing an 

 externally visible tail than is the normal human adult — a fact not 

 without significance. 



If we apply the name of tail to the portion of the vertebral 

 column which is situate outside the trunk of the body, it must bo 

 admitted that from the age of three weeks to that of two months and 



* Seo this Journal, «n(<?, p. 472. 



t ComptcB KtiKiup, c. (1885; j.p. 1100-72. 



