A Contribut. of the Einbryol., Life-history, and Classificat. of the Dicyemids. 85 



Fig. 20. Calotte of a ßhombogen (2.5 mm long) from one side. Propolars plainly 



•• larger than the metapolars. Acctic acid. 



Fig. 21. A very oblique calotte of oue of the longer Rhombogeus (2.5 mm) from 

 the dorsal side. Here the propolars are plainly smaller than the meta- 

 polars. Acetic acid. 



Dicycma microcephalum (figs. 22 — 29). 

 A Nematogen (1.2 mm long) filled with vermiform embryos. Head much 

 more narrow than the body. Osmic acid. 



A young individuai (.44 mm long) represented with all the cells in situ, 

 from the ventral side. Parapolars adjoined by two dorsal and one ventral 

 ectodermal cell. Total number of ectodermal cells 26. Osmic acid. 

 A very small individuai (.2 mm) with the cells loosened by acetic acid. 

 Calotte, parapolars, and three ectodermal cells, seen from the left side. 

 Osmic acid. 



Fig. 26. The calotte of a Nematogen. Head broader than in the fore-going figures. 

 Little difference in size between the propolars and metapolars. No 

 obliquity in the calotte of this species. 



Fig. 27. Cephalic portion of a living individuai. 



Fig. 28. Front view of the calotte. 



Fig. 29. Dorsal view of a Nematogen. Cells somewhat swollen. Osmic acid. 



Piate 3. 



Figs. 30 — 34 Dicyema Clausianuni; figs. 35 — 39 Dicyema macrocephalum ; 

 figs. 40 — 43 Dicycma moschatum. 



Fig. 30 magnified 280/1 ; fig. 40, 1060/1; remaining figs. 465/1. 



Dicyema Clausianum. 

 Fig. 30. A Rhombogen (1.4mm long) from the dorsal side, with all the cells in 



Position. Ectodermal cells 27. Three verruciform cells. Osmic acid. 

 Fig. 31. Calotte of a Rhombogen from the ventral side. Acetic acid. 

 Fig. 32. Optical section of the calotte of a large Rhombogen. The dorsal propolars 



form the tip of the very oblique calotte. Acetic acid. 

 Fig. 33. Ventral side of the fore end of a Rhombogen. Acetic acid. 

 Fig. 34. Side view of the calotte of a large Rhombogen (4 mm long) . No obliquity 



Propolars larger than the metapolars. Acetic acid. 

 Dicycma macrocephalum figs. 35 — 39. 

 Fig. 35. Side view of a calotte, somewhat convex. Parapolars form here no part 



of the head. 

 Fig. 36. A portion of a Rhombogen (1.4 mm) seen from the right side (calotte in 



optical section). The two lateral parapolars follo wed by two dorsal and 



one ventral cell. Acetic acid. 

 Fig. 37. Face view of the calotte of a Rhombogen. The propolars form the 



central part of the cephalic disc, the metapolars its rim. Acetic acid. 

 Fig. 38. Calotte of a young Rhombogen (.7mm long), in which the parapolar 



coUar [pp] is seen to be composed of two cells. Propolars not visible. 



Osmic acid. 

 Fig. 39. Optical section of a young individuai (.25 mm). Osmic acid. 



Dicyema moschatum. 

 Fig. 40. A portion of a Transitional. 



