214 PROCEEDINGS OF THE ACADEMY OF [Feb., 



This appears to be a late development, as it is not found on the sperma- 

 tozoon in the testes, vasa deferentia, or lumen of the penis. 



Emhryological Development. — As stated above, the first maturation- 

 division of the egg occurs in the ovary; fertilization probably takes 

 place in the oviduct; and the second maturation-division is found in 

 the forming capsules. The eggs of capsules just laid always show the 

 two pronuclei with very large nucleoli, as in PI. XIII, fig. 12, and a 

 few hours later the pronuclei are fused as in fig. 13, but the two 

 nucleoli are distinct. The development of the eggs during the first 

 day can be best studied in aceto-carmine. Sections of these and of 

 older capsules may be obtained by piercing the shell with a needle and 

 fixing in sublimate-acetic. The sheU must be removed before embed- 

 ding. The rate of development varies greatly in different capsules, and 

 even among the eggs of the same capsule. Laying occurs in the morn- 

 ing from daylight to ten o'clock. In one case the first cleavage-spindle 

 was found at 10.30 A.M. in one egg of a capsule, in which all the others 

 showed the pronuclei not fused. In other capsules eggs containing 

 the pronuclei were foimd as late as 5 P.M. Two, foiu and eight-celled 

 stages were also occasionally found late in the afternoon. Figure 14, a, 

 was from an egg stained wdth aceto-carmine at 4.30 P.M. There 

 were 6 chromosomes at each pole, as shown in fig. 14, h, obtained by 

 focussing down on one end of the spindle. As in the maturation- 

 divisions, neither centrosome nor sphere could be demonstrated. 



The peculiar positions taken by the blastomeres in 2, 4 and 8-celled 

 stages is showTi in PL XIII, figs. 33-36. Fig. 35 is a reconstruction 

 from five successive sections. Fig. 36 is a section of a 32-celled stage 

 in which the yolk-cells near the group of blastomeres have begun to 



break down in the region x x. The next stage (PI. XV, fig.' 



37) shows a section of an embryo, consisting of a syncitial yolk- 

 mass {y^), distinct from the surroimding yolk-cells and disintegrated 

 yolk-material. The group of blastomeres is always irregular in 

 orm and eccentrically situated, coming to the surface on one 

 s^ide of the yolk-mass. Some of the blastomeres soon begin to wander 

 through the sjmcitium, and may be found dividing at any point. A 

 section of a capsule at this stage frequently shows sections of three 

 or four such embryos. The embryonic yolk-mass gradually increases 

 in size, as may be seen by comparing figs. 37-40, all drawn with the 

 same magnification. The embryo is partly or wholly surrounded by a 

 region of disintegrated yolk-ceUs (fig. 37, a), from w^liich material for 

 the embryonic syncitium is evidently dra^^^l. In some cases whole 

 yolk-cells appear to be taken into the syncitium in amoeboid fashion. 



