132 THE MICROSCOPE. Sept. 



downward with this tube resting on the surface of the 

 water, held in position by many plate-like lobes which 

 are at the end of the tube. 



This larvae grows rapidly, and, after changing its skin 

 several times, comes to the pupa state (fig. 9). The 

 change here is complete. The breathing tubes are now 

 in the thorax and at the extremity of the body is a pair 

 of leaf-like bodies with which it swims. This state lasts 

 only a few days when the pupa skin slits down the back 

 and the mosquito comes forth, stands a few moments on 

 the old skin until its wings are dry; then flies away. The 

 larvae of the mosquito are beneficial as scavengers, for 

 they feed on decaying matter in water. 



Structure of our Hemlock Barks.'-" 



By EDSON S. BAvSTIN. 



Only five species of the genus Tsuga are known; two 

 of these belong to Eastern Asia, one, Tsuga Canadensis, 

 Carriere, is the common hemlock spruce of the Eastern 

 United States ; and the other two, Tsuga 3Iertensiana, 

 Carriere, and Tsuga Pattomana, Brewer and Watson, are 

 natives of the Pacific Coast of Xorth America. All are 

 trees of large size and graceful habit, and the first four 

 are very closely allied, being so similar in appearance 

 that they are with difiiculty distinguished, while the fifth, 

 Tsuga Pattoniana, is somewhat aberrant in its charac- 

 ter, approaching more closely the pines and spruces in 

 its structure. 



Tsuga Canadensis is an abundant species in many por- 

 tions of the Eastern United States and Canada, ranging 

 in its habitat from Nova Scotia to Delaware on the east, 

 extending southward along the Alleghanies to Alabama, 

 and westward along the northern ranges of States and 



■'^For this article aud the illustrations we are indebted to tlie kindness of 

 Mr. H . Trimble, Editor of the American Journal of Pharmacy. 



