302 J- Beard 



not be attached to either view, for so little is known of this species, 

 that it is just possible that M. cysticolum may be a fiinctional herma- 

 phrodite with males. 



True, VON Grafp could detect no male openiugs or male ducts 

 in the supposed female of this species, but, judging by the figure on 

 PI. 13 of bis monograph(4), it seems likely that he did not feel at 

 liberty to make exhaustive use of the scanty material for an exa- 

 mination of this point. A recent study of his figures bas not con- 

 vinced me, that in this case male ducts were really absent, and it 

 is, perhaps, not impossi ble that they were present as small nephridia. 

 The question is, however, still an open one. Nansen maintains that 

 the regulär occurrence of these rudimentary testes in M. cysticolum 

 cannot be accounted for solely by assuming a tendency in the ovaries 

 to develop spermatozoa. But other cases are known, e. g. Bufo, 

 Cymothoe, in which such a tendency is apparent, and in the herma- 

 phrodite M. glahrum ovarian and testicular products may arise from 

 neighbouring cells at first quite alike. It is urged that, if the males 

 of the hermaphrodites were about to become extinct, the ratio of their 

 size to that of the hermaphrodite, on which they sit, ought to be 

 smaller than the corresponding ratio between the male and female 

 of the dioecious species. The size of the males in the former has 

 possibly little to do with this point. Their persistence or extinction 

 depends primarily on their capacity to fulfil their functions. In this 

 argument we again meet the assumption that the encysted forms are 

 more parasitic than the fixed forms', along with the supposition that 

 the absolute size of the male must play the same part in both 

 cases. 



The minute males of the encysted forms suffice, and, therefore, 

 they are preserved. 



That in many parallel cases the dwarf-males find it difficult or 

 impossible to fulfil tbeir appointed duties is proved by their condition 

 in such groups as the Rotifera, where they are verging on extinction. 

 The interesting observations of Weismann & Ischikawa^ on the male 



1 The parasitisra is exactly the same in both, for the cyst is not formed 

 by the parasite, and the question whether or not a cyst be formed probably 

 depends on the position where the parasite affixes itself. A cyst or severa! 

 around the mouth of the host would afFord protection against the parasite at 

 the cost of self-starvation. 



2 A. Weismann & C. Ischikawa, Weitere Untersuchungen zum Zahlen- 

 gesetz der Richtungskörper, in: Z. Jahrb. Abth. Morph. 3. Bd. 1888 pag. 579. 



