folsom: mouth-pakts of anukida maritima. 89 



way that by moving the cover glass they could be rolled into various 

 desirable positions. 



For sectioning, portions of the embryo, or punctured eggs, were im- 

 bedded in hard paraffine. The eggs required at least four hours for 

 thorough penetration. For orienting, Woodworth's ('93) method was 

 employed, but not always with success, as the objects were liable to be- 

 come distorted or even lost. A simpler, but more efficient, method for 

 these particular objects was to orient them under the compound micro- 

 scope with a hot needle in a glycerine-smeared watch-glass of melted 

 paraffine, and to fix them in place by touching the glass beneath witli 

 cold water before hardening the paraffine throughout. When the block 

 of paraffine was inverted under the compound microscope, the imbedded 

 object could be seen through a thin film of paraffine, and a scratch could 

 be made to indicate the plane of sectioning. 



Sections from 5 to 10 /a in thickness were cut with either a Eeichert 

 or a Minot-Zinimermann microtome, fastened with Mayer's albumen 

 mixture, and stained with various reagents, chiefly Delafield's or Klein- 

 enberg's hsematoxylin followed by safranin, Grenacher's alcoholic borax- 

 carmine, and Heidenhain's iron-hcematoxylin. 



General Description of Egg. 



The eggs of Anurida maritima are spherical, from 0.26 mm. to 

 0.38 mm. in diameter, enlarging with age, and at first light yellow, 

 later becoming orange. 



They occur abundantly along the Atlantic coast under stones between 

 tide-marks, and are usually mingled with the conspicuous white exuviae 

 of the parents. 



The eggs of Collembola depart widely from those of other insects by 

 being holoblastic; they are slightly unequal in cleavage. After the mo- 

 rula stage the outer nuclei and accompanying protoplasm migrate toward 

 the periphery, leaving behind yolk masses and also cells which subse- 

 quently prove to be entodermal. The peripheral cells become arranged 

 in two layers : the ectoderm, a continuous superficial layer, with nuclei 

 at regular intervals, and the mesoderm, an inner, less compact layer 

 with fewer and scattered nuclei. Thus there soon results a condition 

 like that derived from superficial cleavage. The ventral plate, or germ 

 band, is formed by migrant mesoderm cells, and, according to Uzel ('98, 

 p. 22, Tomocerus), is first represented by two pairs of isolated thicken- 

 ings, — the procephalic and mandibular fundaments. I have found 



