32 C. 0. Whitman 



a parallel betwenthe Dicyemids and the Ortlionectids ^ Julin remarks ; — 

 »It foUows frolli the observations of Edouard Van Beneden tbat in the 

 case of the Dicyemids the same host generally incloses, all Nematogenic 

 or all Rhombogenic iudividuals ; It is only very seldom that one finds the 

 same host infested with both forms. A fact quite analogoiis holds true 

 of the Orthonectids. Here we find always two female forms in the same 

 host ; but most frequently one finds exclusively males or females in the 

 same Ophiurid. >< (21 , p. 44.) 



I have introduced the Statements of Julin, not because I find them 

 — so far as they concern the Dicyemids — warranted by anything 

 Van Beneden has yet published, but because they claim to be 

 authorized by hisresearches. 



The instances in which the Cephalopod incloses only one of the 

 two forms of Dicyemids are , according to my observations made in the 

 months from December to April inclusive, much less frequent than those 

 in which both are found together. It should be remembered moreover 

 that instances of the first kind may be considerably less frequent than 

 they appear to be ; for it is extremely rare that one can make such a 

 thorough examination of the renal organ that the phrase »not present« 

 may be safely substituted for »not found«. 



Young stages of Rhombogens and Nematogens are liable to be con- 

 founded; and, hitherto, transitional forms have been entirely over- 

 looked. It sometimes happens that the individuals of one kind are con- 

 fiued to one , or at most two or three lobes of the renal organ , and are 

 thus easily overlooked. In view of these sources of error, I am com- 

 pelled to regard with suspicion those cases of isolated occurrence of 

 Rhombogens or Nematogens which were recorded before I became fully 

 aware of the ways in which an examination might miscarry. For the 

 same reasou and others presently to be mentioned, Van Beneden's 

 failure to find Rhombogens in the Cuttle-fish of the Mediterranean can 

 only be accepted as doubtful evidence of the absence of such Dicyemids. 

 That they are to be found throughout the five months from December 

 to April is perfectly certain. 



There are two questions to be answered with reference to the distri- 

 bution of Rhombogens and Nematogens : 



1 . Do they ever occur isolated? 



2. Is their occurrence seasonal, or in any sense periodical? 



The first question may , with considerable certainty , be answered 

 in the affirmative ; and the observations on which this answer is based 

 tend to show that the occurrence of the two forms is not regulated by 



