740 PROCEEDINGS OF THE ACADEMY OF [Oct., 



membranes, are readily penetrated, and that all alcoholic and strong- 

 acid solutions are to be avoided, Flemming's fluid (osmic acid, acetic 

 acid and chromic acid) penetrates easily, but blackens the tissues too 

 quickly. A fixation of three to twenty hours in Zenker's fluid is 

 followed by rinsing in distilled water for fully the same length of time ; 

 then the egg-strings are brought through successive alcohol grades up 

 to 83 per cent. They remain in the latter for several days, then are 

 brought down gradually to distilled water. With each egg-string in a 

 narrow, round-bottomed vial, I take a glass rod and thoroughly crush 

 the egg-string in water after it has been well hardened in alcohol ; thus 

 the eggs are easily freed from each other and none are lost. An 

 aqueous stain is then poured upon them; and for material fixed in 

 Zenker's fluid I found Delafield's hsematoxyline, diluted with an equal 

 volume of water, for two to three hours, the best. The ova, still within 

 the same vial, are brought up through successive grades of alcohol to 

 absolute alcohol, half an hour in each grade; then into a mixture of 

 equal parts of absolute alcohol and xylol ; then into pure xylol. They 

 are then mounted in Canada balsam. These methods have been given 

 in detail, because only after numerous failures have I been able to 

 secure fine preparations. In the structure of the larva much can be 

 determined by study of it in life. And one can best investigate the 

 armature of the proboscis by causing it to be permanently evaginated 

 through treatment with a rather strong aqueous solution of caustic 

 potash; this swells up the whole body. Sections were made of numer- 

 ous egg-strings, but the paraffine imbedding causes great distortion 

 of the cells, and it is necessary to imbed for several hours. The 

 whole mounts of the ova and larvse were the most instructive. 



1. The Early Development. 



The structure of the adult reproductive organs has been previously 

 described by me (1903) in detail, and it is necessary here to recall only 

 a few points to make the development clear. The ovaries are a pair 

 of long tubes extending nearly the entire length of the body, each con- 

 sisting of a longitudinal tube, the "uterus" of the authors, and of very 

 numerous lateral diverticula or pouches, "ovaries" in the narrow 

 sense, each of which communicates by an apertui'e with the uterus. 

 The posterior ends of the two uteri are ciliated, and are termed the 

 oviducts, and these open into the atrium, into the anterior end of 

 which opens also the large receptaculum seminis. The end of the 

 intestine communicates with the atrium, and from that point to the 

 posterior end of the body extends the tubular cloaca, with the cloacal 



