A Contribut. to the Erabryoi., Life-liistory, and Classificat. of the Dicyeiuicìs. 31 



difference between the Nematogens and the Rhombogens. I do not 

 know if an individuai , after having produced and discharged vermi- 

 form embryos, can, arrived at a certain age, become modiiìed and pro- 

 duce infusoriform embryos; or if the Nematogens are originally distinct 

 from the Rhombogens. The latter opinion seems to me more probable; 

 but if it be so, what causes one vermiform embryo to become a Nemat- 

 ogen, another a Rhombogen?« (1, p. 68). To these questions Van 

 Beneden's iuvestigations supplied no answers. 



The first thing in the course of my own observations to draw my 

 attention to the question of the relationship between the two sorts of 

 Dicyemids, was the occasionai finding of a Cephalopod in which, so for 

 as could be ascertained, only Nematogens , or only Rhombogens, were 

 present. If, as Van Beneden's work seemed to show, both kinds bave 

 the same course of development, i.e. botli arise from similar vermiform 

 embryos, how is it that in one Cephalopod ali, or nearly ali, are Rhomb- 

 ogens, in another , ali , or nearly ali, Nematogens ? If within the renai 

 organ these parasites multiply only by vermiform embryos (1, p. 68), 

 how is their propagation provided for in those cases where ali are 

 Rhombogens? 



In Van Beneden's first paper ( 1 ) , I find no allusion to these points : 

 but in bis last (2, p. 209) occurs the following: «I bave succeeded no 

 more than G. Wagener in finding typical infusoriform [embryos] in the 

 spongy bodies of the Cuttle-fish of the Mediterranean. It was in vain 

 that I sought for them during the months of August and September, 

 both at Villefranche and at Trieste. But I was more fortunate in exam- 

 ining Cuttle-fishes from the North Sea , received during the months of 

 October, January, andFebruary. Ali enclosed at least as many Rhomb- 

 ogens as Nematogens ; and the Infusoriform [embryo] of Dinjemina 

 K'óllikeriana [Dicyema gracile G. Wagener) does not diäer perceptibly 

 from that of the other Dicyemids. On several occasions, my father has 

 observed the Dicyemids of the Cuttle-fish : I find in bis notes and sketches 

 that he has always met with the Infusoriforms in great abundance ; 

 it is a Rhombogen of D. KölUkeriana that he has figured and designated 

 under the name Dicyema Krohnii ^ in bis 'Commensaux et Parasites'. 

 How does it happen that neither Wagener nor I bave found the Infuso- 

 riform of the Dicyemina of the Cuttle-fish of the Mediterranean ? That 

 is a question to which I can not reply , unless by the whoUy gratuitous 

 supposition that the Rhombogens appear perhaps only at certain times 

 of the year. « 



In the same number of the 'Arcbives de Biologie', in drawing 



