144 EVOLUTION OF TO-DAY. 



applied, is found to fit the facts marvellously welL 

 " On the hypothesis of evolution this parallelism 

 has a meaning indicates that primordial kinship of 

 all organisms and that progressive differentiation of 

 them which the hypothesis alleges. But on any 

 other theory the parallelism is meaningless, or, 

 rather, it raises a difficulty, since it implies either an 

 effect without a cause, or a design without a purpose." 



Difficulties to be Overcome. 



The task of discovering the history of animals, 

 even when we have the key to the problem in their 

 development, is by no means an easy one. In the 

 first place, difficulties of observation have proved 

 very great. Hardly two animals can be studied in 

 the same way, and it has severely exercised the in- 

 genuity of our scientists to discover how single indi- 

 viduals can be studied. But this difficulty has been 

 gradually disappearing. A second complication is 

 more serious. From the difficulty of observation it 

 has resulted that few of the observations of twenty- 

 five years ago can be relied upon. The older em- 

 bryologists did not realize how very easy it is to 

 make mistakes in their observations on such minute 

 organisms. A little whirling embryo, only semi- 

 transparent, is a very difficult object to study, even 

 with the best methods and conveniences. It is 

 therefore to be expected that the first observations, 

 made with imperfect instruments, should be very 

 faulty. And, moreover, the simplest principles of 

 the subject were then unknown, and, with nothing 

 for a guide, the early observers did not even know 



