410 WILLIAM A. HASWELL. 



Development. 



In the case of P. Dolirnii, Zscliokke (20) states tliat the 

 formation of egg's begins in the posterior proglottides of the 

 strobila. In the form now under consideration this is not the 

 case, eggs only occurring in well-developed free proglottides. 



The only recorded observations on the development of any 

 member of the genus appear to be a few notes on P. thridax 

 by Moniez (14, p. 28). I can trace no correspondence what- 

 ever between the statements there made and what I have been 

 able to observe in the species from Cestracion. 



The primary uterus contains only eggs with vinsegmented 

 ova. The entire egg is in the form of a thick spindle about 

 '045 mm. in length and '021 mm. in greatest breadth. The 

 shell is at this stage not yet fully solidified, so that the 

 shape is readily modified by pressure, and the eggs tend to 

 adhere together in masses. The shell consists of two distinct 

 layers — an outer homogeneous and an inner made up of fine 

 fibrillte — which run in the direction of the long axis of the egg. 



The completed egg in the primary uterus contains (1) the un- 

 segmented ovum ; (2) a large number of small, bright globules 

 (3) one, or, more commonly, two, larger rounded masses. 

 The last two are the substance of the vitelline spherule. 

 When the eggs are acted upon by any weak acid the small 

 globules tend to run together into larger (2 [14], p. 28) masses, 

 and eventuall}^ these pass out through the shell at the ends of 

 the egg, so that in preparations fixQd and stained by any of 

 the ordinary methods this constituent of the egg becomes 

 completely lost, there being left behind merely some irregular 

 granular matter, in wdiich, presumably, the globules were 

 enveloped. These globules, from their appearance and 

 behaviour, are most probably composed of oily matter. 



The larger bodies derived from the yolk (see fig. 20) are of 

 an entirely difFei'ent character. They are solid masses luiving 

 the central hihim and concentric lamination characteristic of 

 the calcareous corpuscles. They become coloured, though 

 not strongly, by staining agents, the central mass colouring 



