302 



SCIENCE 



[N. S. Vol. XXXIII. No. 843 



erable antiquity, and the uppermost deposits 

 unquestionably of modern date which alone 

 can be invoked as evidence of recent subsi- 

 dence. It would appear, also, that he has not 

 clearly understood my paper; for it is other- 

 wise difficult to account for such statements 

 as " the hypothesis of a fluctuating high-tide 

 level has no possible application " to the bo- 

 tanical evidence of present subsidence as pre- 

 sented by Dr. Davis; or that the hypothesis 

 " has no bearing whatever on most of the evi- 

 dence which has been offered." Surely if the 

 height of ordinary high tides gradually rises 

 one or more feet as the result of changes in 

 the form of the shoreline without change in 

 the level of the land, this increase in tidal 

 height will produce all of the phenomena 

 which would be produced by actual subsidence 

 of the land, " now going on." The task which 

 confronts the student of shoreline changes in- 

 volves a discrimination between different 

 causes producing like results; and the best 

 method of making such a discrimination is, 

 in the opinion of the writer, to deduce the 

 character and magnitude of the results which 

 each hypothetical cause is theoretically capable 

 of producing under the varying conditions 

 which exist along an irregular coast, and 

 then to compare the deductions with the 

 actual phenomena as observed in the field. So 

 far as I have carried such an analysis for the 

 Massachusetts coast, the evidences of sup- 

 posed recent subsidence are all capable of 

 interpretation on the basis of a fluctuating 

 high tide surface; whereas physiographic 

 features of much importance seem incom- 

 patible with the theory of continued recent 



subsidence. 



D. W. Johnson 



"^ MIASTOR AND EMBRYOLOGY 



Eeproduction by insect larvse, a form of 

 parthenogenesis known as pedogenesis, is ex- 

 tremely interesting. The writer was fortu- 

 nate last fall in finding, in the partially de- 

 cayed chestnut bark of a rail fence, numerous 

 Miastor larvae, forms not previously recog- 

 nized in this country, though several species 

 and representatives of allied genera have been 

 studied by a few Europeans. Miastor larvse 



and their allies should be of great service to 

 teachers of zoology and biology, since they 

 admit of the study at first hand of this inter- 

 esting phenomenon. It is possible, with a no 

 more elaborate outfit than an ordinary stu- 

 dent's microscope equipped with a three- 

 fourths objective, a microscopic slide and a 

 few cover-glasses, to observe the vital activities 

 of the young larva, to see the muscular, res- 

 piratory, digestive and nervous systems, tO' 

 identify the ovaries and to watch the gradual 

 development of the semi-transparent embryos- 

 within the body of the living mother larva. 

 Furthermore, these forms are well adapted to 

 more exact histological methods, being soft 

 and therefore excellent subjects for serial sec- 

 tions and stains, particularly as it is compara- 

 tively easy to secure from one colony a series 

 of individuals representing different stages of 

 development. 



Aside from the interest attached to their 

 morphology and biology, there are other con- 

 siderations which should appeal strongly to 

 the teacher of zoology. These larvs are widely 

 distributed and, with an understanding of 

 their habits, there should be little difficulty in 

 finding them. They are small, and a piece of 

 wood six inches long, three inches wide and 

 half an inch thick, may contain or produce 

 enough material for a fair-sized section or 

 class. The larvse are prolific and, under favor- 

 able conditions, would probably multiply at 

 any season of the year. This is certainly true 

 of the fall, the early winter and the spring.. 

 They can be kept alive for at least a month in 

 microscopic cells, and with care a larval gen- 

 eration will develop in such restricted quar- 

 ters. We have kept larvse healthy and multi- 

 plying for nearly three months with nothing 

 more elaborate than a moist piece of decaying 

 wood clamped lightly to an ordinary micro- 

 scopic slide and kept in a moist, dark box. 

 Many of the larvse were content with condi- 

 tions on the surface of the wood, next the 

 glass, and were therefore easily observed. 

 These remarkable larvse are very hardy; pro- 

 longed dryness simply results in a suspension 

 of activities, while they are quite resistant to 

 an abundance of moisture. Embryos will con- 

 tinue their development in mother larv» even 



