A Contribut. to the Euibryol., Life-history, and Classificat. of the Dicyemids. 25 



raoving- freely in the renai fluid. In this condition it is easy to see, in a 

 lobed calotte resembling that in fig. :'5, that two lobes are ventral and 

 two dorsal. When specimens are killed in acetic acid, or by any other 

 means, and covered by a glass, the calotte is exposed to pressure, 

 unless protected by supports placed under the cover. Such pressure is 

 ali that is required, especially with individuals lying sidewise, to in- 

 duce appearances of the same nature as Van Beneden has described. 



With respect to the number of parapolar cells, it is easy to be mis- 

 led, particularly in adult forms. The two lateral angles of the para- 

 polars (fig. 36) are turned strongly toward the ventral side , and the 

 dorsal notch left between them is filled by the fore ends of two ecto- 

 dermal cells, which extend far forward , but ne ver reach — so far as I 

 bave observed — the polar cells. It is these two cells that , added to 

 the two lateral parapolars , raake up the four parapolars of Van Bene- 

 den's description. It is not always easy to see, in the larger examples, 

 the anterior limifs of these two cells ; but the development, and the 

 whole series of younger stages, bear witness to the fact that this species 

 agrees with ali others at present known, in respect to the number of 

 its parapolar cells. In fig. 38, from a young individuai only .7mm long, 

 a complete parapolar coUar is seen, formed of two lateral halves, joined 

 in the median dorsal and median ventral line. From the same figure it 

 is plain that there are two dorsal and two ventral metapolars. The pro- 

 polars, not represented in this fig. lay in the same piane with the meta- 

 polars , not projecting beyond them , as seen in the younger form of 

 fig. 39. I think the parapolars never take so conspicuous a part in the 

 formation of the head as Van Beneden has represented. Cases similar 

 to bis figures bave been seen, but they appeared to me to present un- 

 natural forms due to swelling. 



The number of verruciform cells varies from to 5. They may be 

 quite conspicuous, but I bave never seen instances of their projecting 

 strongly beyond the other ectodermal cells. 



With the above exceptions . Van Beneden has given a very accu- 

 rate description of the calotte: »The calotte is bere a cellular piate 

 formed of flattened cells. This piate is very obliquely placed at the 

 anterior extremity of the endodermal celi ; it looks toward the ventral 

 side. In well developed individuals it is sometimes piane, but more 

 frequently concave (?). In ali young individuals it is convex. It is 

 formed of eight polar cells disposed in a centrai set of four cells and a 

 peripheral set of the same number. When the calotte is seen from the 

 face, the centrai cells show a triangulär form; the peripheral cells form 



