A Contribut. to the Embryol., Life-history, and Classificat. of the Dicyemids. 19 



mSepiaofficinaUs, tban from either of the other specves thus far describ- 

 ed. Under the persuasiou that these two species were one and the same, 

 Van Beneden was led to attribute to a calotte belonging to D. trunca- 

 tum characters that are wholly foreign to it. He affirms that this calotte 

 is composed of nine cells, and in bis fig. 6, PI. 1 . he has actually delin- 

 eated this number of polar cells, which certainly exceeds by one the 

 number placed there by nature. This species bears an octaraerous ca- 

 lotte, while that of the associate species is enne^merous ; and this fact 

 alone proves that their Separation is well founded. A glance at figures 

 48_50 [D. gracile) and 53 — 59 [D. truncatum] , will make it evident 

 that the two species are quite distinct in many other respeets. They are 

 distinguished by the total number of cells , by the length and general 

 appearance of the body , by the form and the character of the two cau- 

 dal cells, by the shape of the cephalic enlargement, and by the share 

 taken in its formation by the parapolars. Most of the distinctions seen 

 in the adult forms are also to be found in the young, and even in the 

 unliberated embryo, so that there remains no ground for the supposition 

 that D. truncatum is only a younger form of D. gracile. 



Van Beneden describes the »renflement céphalique«, represented 

 in the figure just referred to, thus : 



»In Dicyemina K'óllikeriana of the Cuttle-fish there are nine polar 

 cells disposed in two sets. These cells are very small, compared to the 

 polar cells of Dicyema and Dicyemeìla. They form together a very 

 granular , opaque body, capping the anterior extremity of the endo- 

 dermal celi. But this coiffe is very eccentrically placed in the cephalic 

 enlargement (voir pi. 1 , fig. 6). It is strongly inclined toward the ven- 

 tral side. In young individuals, the nine polar cells forming this coiffe 

 are placed in the same oblique piane with respect to the axis of the 

 body. This piane looks downward and forward , when the organism is 

 placed in a normal position. The head appears cut in front by an ob- 

 lique truncation. The first set of polar cells comprises four conoid or 

 pyramidal cells much smaller than those of the second set ; and two of 

 these are smaller than the other two , and turned toward the ventral 

 face. In the second set one counts five prismatic cells placed, with 

 respect to one another and to the centrai polar cells of the coitfe, as in 

 the species of Eledone moschata. 



As the individuai increases in size , the polar coiffe becomes rela- 

 ti vely more extended and its characters so modified that it becomes 

 more like the polar organ of the Poulp and Eledone.« (p. 18 and 19.) 



From this it appears that Van Beneden regarded B. truncatum as 



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