181 



the largest specimens examined during February and March may not 

 have attained their full growth. 



It is more than probable that M. hrevicirrum also agrees with the 

 three species which I have studied. According to v. Graffs this spe- 

 cies when only 24 mm in diameter »has the seminal vesicles filled with 

 spermatozoa whereas the eggs are but little developed« and adds that 

 »it may be concluded that the male apparatus is earlier developed than 

 the female«. 



All the free-living species of the genus Myzostoma will probably 

 be found to agree with the forms which have just been considered. 

 "We may, perhaps, go even further and include the cysticolous species 

 under the same law. Of the ten swelling- or cyst-producing spe- 

 cies described by v. Graff the sexual condition of the specimens is 

 mentioned in seven. Two of these [M. petitacrini and M. deformator) 

 are hermaphrodites and appear to agree with the free -living species 

 except in the unilateral development of the testes. In five species 

 each cyst contains a large female and a small male individual. In one 

 of these [M. cysticola) the large female has rudiments of testes. This 

 fact together with his above- quoted observation on M. brevicirrum, 

 led V. Graff to conclude that the young of the cysticolous species 

 associate in pairs and bore their way into the arm-joints of the Cri- 

 noids together. He supposed that in both individuals the testes de- 

 veloped first but that in one (the female) the male reproductive organs 

 degenerated or entirely disappeared when the ovaries made their appea- 

 rance. This hypothesis is in perfect accord with my own observations 

 on the free-living species. 



Unfortunately I have been unable to secure specimens of the cy- 

 sticolous species , but in M. pulvinar , which occurs in the alimentary 

 tract of Antedo7i 'phalangium the sexual conditions appear to be iden- 

 tical with those of the extreme cysticolous forms like M. inflatory Graff, 

 M. Murrayi, Graff, etc. As Prouho has shown, M. pulvinar occurs 

 in pairs, each consisting of a large female and a very small male. Al- 

 though I have sectioned a number of specimens I am unable to main- 

 tain that the males are really young individuals which will ultimately 

 develop into females after passing through an hermaphrodite stage. 

 Still I have seen nothing to render such a supposition improbable. 

 The diminutive males have traces of the uterus and in one case I 

 found what I took to be a proliferation of peritoneal epithelium like 

 that of the ovaries in the young M. glabrum. This very imperfect de- 

 velopment of the ovaries may be attributed to the fact that all the 



8 L. V. Graff, Report on the Myzostomida collected during the voyage of H. 

 M. S. Challenger during the years 1873—1876. Zool. Chall. Exped. Part. XXVII. 

 1884. p. 1—52 and Suppl. p. 1—16. PI. I— XVI. 



