A Contribut. to the Embryol., Life-history, and Classificat. of the Dicyemids. 21 



never found any uuiform iuequality such as Van Beneden insists on 

 between the dorsal and ventral polar cells, I am compelled to determine 

 the direction of inclination by reference to the parapolars , and there- 

 fore to regard the figure as seen from one of its lateral faces. If I am 

 correct in this , the figure represeuts a case of obliquity fully analogous 

 to that seen in fig. 57, showing that it may occasionally be dextral, or 

 sinistrai , instead of ventral. This irregularity in the direction of tlie 

 inclination, of which I bave seen a considerable number of instances, 

 and the inconstancy of its occurrence presently to be noticed , lead to 

 the conclusion , already expressed with reference to some of the fore- 

 going species, that very little importance can be attached to this phenom- 

 enon as a specific character. In order either to remove or explain the 

 incougruity between this opinion and that emitted by Van Beneden, 

 I bave made repeated examinations with special reference to this point. 

 The result has been that I bave found it necessary , first of ali , to ex- 

 plain the incongruities between my own observations ; for what was 

 recorded as the rule one day, appeared to be the exception the next. 

 After examining carefully a large number of individuals obtained from 

 a Cuttle-fish Mar. 14, I made the following note: 



»As a mie the inclination is hardly tu be recognized, and I doubt if it be a 

 normal feature.« 



A later note reads thus : 



»I find that there is a plain obliquity in many heads ; but it is by no means 

 Constant, nor can I say that it exists in the majority of cases.« 



That the same species of Dicyema varies sometimes considerably 

 from one Cephalopod to another, is a fact which has forced itself upon 

 my attention in nearly every species that I bave examined ; and it is 

 more on account of its general importance than its special significance 

 that I bave gone into details with the case in band. According to my 

 observations, theu, obliquity of the calotte is exceptional in some cases, 

 and more or less general in others; it may be dextral or sinistrai, but 

 is more frequently ventral. 



With reference to the arrangement of its cells . this calotte difiers 

 in one particular from other octamerous calottes. The entire difterence, 

 however , may be explained as the result of a rotation of the metapolar 

 disc on its axis through 45'^ , the propolar disc maintaining its originai 

 Position. This rotation of an octant makes two of the metapolars lateral, 

 one dorsal, and one ventral (figs. 58, 54, 57) . The arrangement of parts 

 thus becomes similar to that of a flower, the perianth of which consists 

 of two cruciform whirls of leaves alternating with each other. 



