608 W. S. NICKERSON, 



the uterine eggs is thin and delicate and geuerally shrivelled iu my 

 speciniens except iu the case of those eggs which were nearly ready 

 to be discharged. These have retained their form and measures about 

 98 X 60 /*'? the outline being elliptical, the two ends alike, and the 

 hne of Separation of the lid not evident. I have not traced the de- 

 velopment of the erabryo but have made some observations upon the 

 fully forraed embryos just emerged or ready to emerge frora their 

 Shells. Sections of such embryos are represented in Figs. 17 — 21. 

 Fig. 17 represents a nearly sagittal section of an embryo already 

 freed from the shell and contained in the sulcus about the base of 

 the retracted neck (cf. Fig. 9). The oral cup or funnel, the pre- 

 pharynx, pharynx and intestine are shown already formed and in 

 relations such as may be considered typical of the family Aspido- 

 boihridae. The large shaded area near the posterior end represents a 

 posterior sucker cut one side of its central depression, the next section 

 (Fig. 18) passing thro' its centre. Above the posterior sucker there 

 is shown in Fig. 18 an oval clear space having somewhat the appear- 

 ance of a highly vacuolated Single cell. Transverse sections shovv that 

 two such cavities exist side by side. It is safe to assume that these 

 are the rudimentary excretory vesicles. 



Fig. 19 represents parts of two adjacent nearly transverse 

 sections thro' the region of the pharynx and shows especially the 

 tufts or Clusters of cilia which make here an incomplcte band around 

 the embryo. On the ventral side the cilia tufts are lacking. Portions 

 of the same band in other embryos are shown in longitiidinal section 

 in Figs. 17 and 21. A comparison of Figs. 20 and 21 will make 

 clear the relations of these tufted cilia. Fach Cluster arises from a 

 central crater like depression which is enclosed by a circular rim like 

 ridge in which nuclei are present. In the case shown in Fig. 20 there 

 are two nuclei as I have also observed to be case in some other in- 

 stances but whether more than one are present in all cases I have 

 not determined. Cell outlines I have becn unable to distinguish. A 

 Cluster of similarly ciliated cells is also present at the posterior end 

 of the embryo as represented in Fig. 17 but I have not determined 

 their exact number. 



The cells from which the cilia arise form very evident thicken- 

 ings of the integumeut which elsewhere is thin and very nearly 

 homogeneous in appearance. In places however I have been able to 

 distinguish what appear to be very indistinct nuclei in this layer as 

 shown in Fig. 17 (w). Their presence together with the abseuce of 



