A Coutribut. to the Embryol., Life-history, and Classificat. of the Dicyemids. 47 



depend ou the age of the Dicyemid. I am unable to assign auy causes 

 for such a change. Possibly it is in some way connected with the ex- 

 haustion of nuclear substance, or some dement of this substance. 



Germ-cells. — It has already been shown that vermific germ- 

 cells diflFer, as a rule, conspicuously in size from infusorific germ-cells. 

 In Dicyema moschatum I find the cells of the first class about two thirds 

 as large as those of the second class. The average size of infusorific 

 germ-cells, as given by Van Beneden, is .021 mm. while vermific 

 germ-cells are said to vary between .012 mm and .014 mm. As the 

 difference in size between these two kinds of cells furnishes one of the 

 means of recognizing transitioual phases, a few cases may bere be given, 

 supplementary to those already described. 



Dicyema moschatum. — 1. Fig. 62, PI. 5, represents one of the 

 smallest (.0045 mm), and figs. 63 and 64 two of the larger germ-cells 

 (.0085 mm] found in the same Nematogen. Both of the larger cells had 

 attained their full size and were preparing to take the first step in cleav- 

 age, as indicated by the presence of spindle-fibres in the nucleus. 

 These figures were drawn from acetic acid preparations , and care was 

 taken to select such cases as could be said with considerable certainty 

 to be entering upon a developmental, or cleavage division , rather than 

 a multiplicative division. 



2. Feb. 9. A small Eledone in which only Nematogens were 

 found. In one individuai containing a single embryo, the germ-cells 

 ranged between .004 mm and .010 mm; in another (2.90 mm long) 

 containing several embryos the numerous germ-cells varied between 

 .004 mm and .008 mm. Both individuals were primary Nematogens, 

 as shown by the single free nucleus. 



3. Apr. 4. A secondary Nematogen, inclosing numerous embryos, 

 and germ-cells varying between .003 mm and .008 mm. Osmic acid 

 preparation . 



4. Apr. 11. A long Nematogen inclosing in the posterior half em- 

 bryos and germ-cells (.004 mm to .009 mm) ; in the anterior half numer- 

 ous fusiform and otherwise elongated cells which were uearly ali in 

 process of multiplicative division. To find germ-cells in this conditiou, 

 it is only necessary to take fresh Dicyemids and examine them while 

 the acid is penetrating. Multiplication by division is certainly not a 

 rare phenomenon although Van Beneden states that he never saw it. 



Dicyemetmea Eledones. — 1. Mar. 10. A primary Nematogen, 

 4.2 mm long, contained few embryos and germ-cells scattered aloug the 



