Thk Microscope. 31 



■suggestive hints that the good teacher and the learned writer 

 knows so well how to give, and that are so welcome to the earn- 

 est pupil. For instance, under the fresh water brown Hydra, H. 

 /usca, the author directs : I.— Pour the alcoholic specimen into 

 a watch glass in water ; place on a dark ground, Obesrve: 1, 

 body cylindrical in form ; 2, the long threads, tentacles, situated 

 at the oral end; 3, the blunt aboral end or base; 4, in some speci- 

 mens on the side of the body near the aboral end a bud. II. — 

 Slice across the body with a scalpel at the largest place, cut again 

 across the cut end, removing thus a cross section. Mount the 

 section in water, and examine with a hand lens. Observe: 1, 

 the body is not solid, but hollow ; 2, the skin or wall of the body 

 is composed of two distinct coats, viz. : a, an outer coat, thin, 

 smooth and regular — ectoderm; b, an inner coat, thick and 

 irregular — endoderm ; '' with more that, like the foregoing, might 

 easily be overlooked ' by the beginner who is here told how to 

 look and what to look for. Among several marine animals, 

 Prof Osborn in this commendable way treats of the angle worm, 

 the fresh water mussel, the slug, the pond snail, the cray fish, 

 •the sow-bug, the spider and the grass-hopper. 



While the little pamphlet is primaaily intended for college ' 

 •students attending a course of lectures it may be used with as 

 good results by the pupil that has himself for a teacher ; with 

 it to direct him he will be helped to observe and to compare. Of 

 the nineteen animals included, eight are marine, four aquatic and 

 ■seven terrestrial, so that no one, wherever he may be, need ever be 

 ■at a loss for material to study. 



C°RRESP°riDmCE 



^ 



UKD^.e<,^ 



Editor The Microscope: — 



"Amateur " has written so discriminatingly and instructively 

 for the year past that his strictures upon the Wenham binocular 

 in a late number were a real surprise. Having no practical ac- 



