1 882.] Zoology. 813 



the species by written characters or descriptions is beyond my 

 powers. But no one has ever seen so many of the type-speci- 

 mens of the species as I have, nor given more time to the sys- 

 tematic study of these genera. * * * 



" It is noticeable that the herbarium of Nees von Esenbeck for 

 Aster is not referred to. I cannot ascertain what has become of it. 

 But the types of several of his species, or specimens named by 

 him, have been met with in other herbaria, especially in that of 

 Lindley, and that of Schultz, Bip., the latter now a part of the 

 large collection of Dr. Cosson. As to Asters, I do not here 

 attempt anything beyond a report of the main results of the study 

 of certain principal herbaria ; and I leave the high northern and 

 far western species out of the present view." 

 ZOOLOGY. 



Habits of Fresh- water Crustacea. — No one branch of bio- 

 logical study is now bringing forth more interesting and every 

 way useful results than embryology. Throwing "light as it does, 

 not only on questions of classification and theoretical biology, 

 but also on the application of such theories to practical life, 

 this new science may be termed at once the root and most 

 typical fruit of a revolutionized biology. No other science fur- 

 nishes a better illustration of the value of minute, accurate study 

 of the most common and apparently insignificant facts. Sets of 

 isolated facts evolved by conscientious study of different men 

 spring suddenly into line when once the clue is found, and the 

 result may be a new law which renders all these facts eloquent. 



To the systematist the merely external study of life histories is 

 of greatest value as a check against redundancy in classification, 

 and furnishes the only reliable method, among lower forms at 

 least, of setting the bounds of species. 



Many eminent monographers have beeVi obliged to considera- 

 bly augment the nomenclature of their specialty with names 

 which, later, have proved to apply simply to larval or immature 

 forms, on account of the impossibility of following the whole life 

 history of each individual. 



To confine ourselves to the class Crustacea, many instances of 

 this sort could be recounted. The best known is perhaps that of 

 the common Cyclops which in the earlier' days of carcinology 

 enjoyed as many as three names between its exclusion from the 

 e gg and maturity. The discovery of the earlier stages in the life 

 °f Cyclops opened a new vista in the whole subject, and now we 

 recognize a " Nauplias stage" in the life-history of nearly every 

 crustacean. 



It has been more recently discovered that similar opportunities 

 tor error are afforded by the difficulty of distinguishing the ulti- 

 mate stage in an animal's life. It has been shown that the func- 

 tions of reproduction are anomalous in the lower animals. Espe- 



