EMBRYOLOGY OF CLEPSINE. 217 



and sometimes chromic acid (^^ per cent.), followed in each case 

 by weak, strong, and absolute alcohol. 



c. Imhedd'mg. In clove oil till thoroughly permeated. Im- 

 bedded in paraffin to which a little pig^s lard has been added. 



d. Catting. Leyser's microtome. 



e. Mounting. Sections freed from paraffin by means of ben- 

 zine Mounted in balsam. 



3. Surface views of the germ-hands. Eggs treated with 

 chromic acid 5 — 10 hours show well the linear arrangement of 

 the nerve-cells. For views of the inner surface it is necessary 

 to free the germ- bands from the yolk. This is done in the 

 following manner : — The fresh embryo is placed in a drop of water 

 upon an object-slide ; a little acetic acid (as much as will adhere 

 to a needle) is added, and all placed under the dissecting lens. 

 With a pair of needles a rupture is made along the dorsal side. 

 By careful manipulation of the needles the embryo, in most cases, 

 can be led away from the yolk and stretched out on the slide. 



After partially removing the water by means of a bit of blotting 

 paper, a few drops of osmic acid are added, with care not to 

 disturb the object. At the end of an hour the embryo is washed 

 and stained with Beale^s carmine. It is again washed and 

 treated with weak, strong, and absolute alcohol. Mounted in 

 balsam or glycerine. During all this the object is )iot once 

 removed from the slide. 



I. OEIGIN AND GROWTH OF THE EGG. 



a. Formation of Primitive Egg-cell. 



According to Leydig (t-H-'s)j ^^^^ ^''^^ ^'"^ first to give atten- 

 tion to this matter, the egg-string is a nucleated protoplasmic 

 mass. Around these free nuclei no cell-limits are visible. The 

 formation of the egg-cell is compared, to the cleavage process. 

 " Die Bildung der Eier in ihm (egg-string) findet statt nach 

 Art der Furchungskugeln, d. h. man sieht freie blaschenfurmige 

 Kerne, dann um diese einzelne Elementarkorperchen unregel- 

 massig gelagert ; mit Zunahme derselben bilden die Hiiufchen 

 der Elemeutarkorner mit dem eingechlosseneu Keru eine lang- 

 lich-kugelige Form, es tritt eine membran auf." 



Ludwig (VV) accepts this view and extends the same to 

 other Hirudinea. Leuckart dV"-^), on the other hand, speaks of 

 the egg as arising from a ready formed cell. Robin ('i") has 

 maintained a singular theory of the egg- formation in the Hiru- 

 dinea. According to this theory the egg forms, after copula- 

 tion, withm a spermatophore. The spermatophore with its 

 inclosed ovules is called an " ovo- spermatophore.^^ Although 

 Leukart (-jj-„'4) pointed out Robin's error as long ago as 1863, 

 the latter still holds fast to the same theory in his last great 



