The Microscope. 213 



divesting of the rotifer of a very thin and hyaline pellicle, and sees 

 no reason why this would clash with the theory that the adultt ube is a 

 secretion, since it would assist the flow of the fluid in a proper direc- 

 tion for the purpose it has to serve. Following these movements the 

 rotifer retreats within the cup-like tube, assumes the form of a puff- 

 ball, and remains apparently quiescent for some time; hardly per- 

 ceptible changes are, however, going on, (fig. 3.) Four hours later, 

 the organism is visibly enlarged, the cilia have become arranged 

 parallel to each other, and protrude like a small bush, (fig. 4.) 

 These are afterwards absorbed, and an hour later partly developed 

 arms are seen (fig. 5.) After this development goes on and is com- 

 pleted by the following morning. The development is not always 

 the same in point of time in different individuals, one act being, per- 

 haps, prolonged, while another is greatly shortened. 



As to the length of time after birth when reproduction will 

 take place, a series of observations gave the aiverage as 6^ days. 



The largest number produced by one individual was five ; the 

 smallest three, — more frequently four completed the progeny. 

 While the male of this rotifer has not been discovered, Harris found 

 one individual with a pear-shaped cavity near the angle where the 

 posterior portion rapidly narrows ; and in this space were bodies in 

 rapid motion, and which may have been spermatozoa. This creature 

 did not settle down like the others, but led a wandering life ; it 

 increased but slightly in size, and its development was arrested at a 

 very early age. It lived about thirty-six hours and was not seen to 

 take any food. 



Pathogenesis was seen to take place to the fourth generation; 

 the last individuals containing ova, which did not develop, the indi- 

 viduals dying after a normal life, without issue. The allotted span 

 of life is from 13 to 14 days. 



The Development of Bone. — Dr. W. X. Sudduth read before 

 the International Medical Congress a paper on the above subject, 

 presenting at the same time several sections of new bone under the 

 microscope. He reviewed the various processes by which bone is 

 developed, and stated his belief that another classification of the 

 methods by which growth occurred, and suggested the word 

 "interstitial" as having special reference to ossified products which 

 came under the classes heretofore in general use, namely: intra- 

 membranous, intra-cartilaginous, and sub-periosteal. There has 

 been an attempt on the part of nature at the age of one or two 



