148 NATURE STUDIES. 



Fourthly, if these likenesses, be admitted it logically 

 follows that they must be susceptible of explanation. 

 The only feasible and rational account of the resem- 

 blances in question, is that which, through the aid of 

 the theory of evolution, attributes the likeness to 

 a common origin or descent, as it attributes the 

 differences to modification and adaptation to special 

 ways of life. If this explanation be admitted, it 

 follows, fifthly, that the entire vertebrate series, from 

 the lancelet to man, has been evolved from a root-stock 

 represented to-day by the sea squirt's larva. The 

 Tunicata, in this view, are the far-back progenitors 

 of the vertebrate tribes. 



One has heard frequent allusions to the so-called 

 " base origin " of man as attributed by evolution to 

 the sea squirt larva, and this usually from persons 

 unacquainted with the marvellous details of parallel 

 development in sea squirts and in the lancelet. But 

 such persons forget that, traced back to its ultimate 

 beginnings, the human germ itself is a mere speck of 

 protoplasm about the y|-y-th of an inch in diameter, 

 and indistinguishable in any fashion from the egg of 

 lancelet or of sea squirt. Moreover, at a certain stage 

 in man's early history, the developing germ resembles 

 tolerably closely that of sea squirt and lancelet, as, later 

 on, it has characters common to all quadrupeds, and 

 only as an ultimate phase exhibits the special features 

 of the human type. In a word, the hard facts of 

 development exist, whether we like them or no ; and 

 they alone are wise who can reflect, calmly and placidly 



