A contrìbut. tu the Embryol., Lite-bis tory, and Classitìcat. uf the Dicyemids 1] 



cases, and in one (Fig. 19) the propolar cells are fiilly equal in bulk to 

 the metapolar. 



Fig. 20, representing one of the largar indi viduals, seen from the 

 right side, agrees with Van Beneden's account in showing very little 

 obliquity, and in having the ventral cells smaller than the dorsal; but 

 differs in having the propolar cells decidedly larger than the metapolar. 

 In this latter respect, the figure rei)resents a case which is neither the 

 most frequent nor the most exceptional. This and other like instances 

 noted at the same time, appear to show that the inequality in size 

 between the first and second sets of polar cells has not the uniformity 

 requisite to give it auy vaine as a specific character. 



Again , in regard to the obliquity of the calotte , every degree of 

 Variation may be found between Fig. 20 and Fig. 21. Fig. 21 shows a 

 perfectly normal and well preserved head of one of the largest individ- 

 uals (2.5 mm), seen from the dorsal side. Nearly ali the longest spee- 

 imens found at the same time exhibited this extreme obliquity, and 

 some of them a stili greater degree. Widely as this calotte differs in its 

 general aspect from that of Fig. 1 9 , a comparison of the two will show 

 that the whole differeuce may he explained as a forward movement of 

 the dorsal polar cells resulting from the un equal growth of thedor- 

 sal and ventral sides of the parapolar cells. As the dorsal propolar cells 

 [adp] are carried forward, they must at the same time dro}) downward 

 in order to preserve their connection with the ventral cells. This will 

 be seen from Fig. 32 , a vertical section of a less plagiotropal calotte. 

 If the tilting ot the celi adp be carried a little further by pushing for- 

 ward the celi pdp , the relative position of the cells would be the same 

 as seen in fig. 21, 



2. Dicyema Clausianum E. v. Ben. Pigs. 30 — 34, PI. 3. 



Found exclusively in Octopus macropus Risso. Ca- 

 lotte octamerous; orthotropal in the youngest indi- 

 viduals; in the larger examples raay be per fectly orthot- 

 ropal, or more or less plagiotropal; generally broader 

 than long, well marked off from the body. 



The propolar cells may be a little smaller than the 

 metapolar, or vice versa. No marked and Constant dif- 

 ference in size between the ventral and dorsal cells. 



The 2 lateral parapolar cells alternate with the 2 

 proximate ectodermal cells (one dorsal the other ventral). 



Verruciform cells — 5. 



