176 



Termiforin embryos. By this time one or more males from some other 

 Octopus find their way into the kidney and discharge their spermatozoa. 

 These spermatozoa enter the axial cells of the nematogens and fertilize 

 the germ-cells aggregated in the infusorigens. From these cells deve- 

 lop the males which may in turn fertilize either the remaining nema- 

 togens in the"same kidney or migrate to other Cephalopods. As in so 

 many other cases in the animal and vegetable kingdoms the males make 

 their appearance when the conditions of life become unfavorable, viz. 

 after the kidney is well peopled with Dicyemids and food is less abun- 

 dant. These unfavorable conditions are perhaps still further aggravated 

 by changes in the renal metabolism of the Octopus when it is about 

 4 cm long. This view of the lifehistory oi Dicyema dispenses with the 

 postulate of an intermediate host and an adult form of which Dicyema 

 is only the larva. The Octopus of the Pacific coast, at least in its youth, 

 is more or less gregarious. I have taken more than fifty small individuals 

 (1 — 5 cm long) in an area of less than an acre in San Diego Bay. 

 Under such conditions even minute parasites like Dicyema would, per- 

 haps, find little difficulty in migrating from one Octopus to another. 



While it simplifies our views of the life history of the Dicyemids, 

 the above interpretation complicates the question of their systematic 

 affinities. Their mode of reproduction would appear to be very unlike 

 that of the flat-worms from which many zoologists derive them. In my 

 opinion, it is a step backwards to place the Dicyemidae in a separate 

 subkingdom, as did van Be ne den when he called them Mesozoa. I 

 believe, however, that their structural and developmental peculiarities 

 entitle them to a more independent rank than that of an appendix to 

 the Platyhelminthes. 



Bibliography. 



1881. Balfour, F.M., A Treatise on Comparative Embryology, 2 Vols. 1881. 



1882. Julin, C, Contribuxions à l'histoire des Mésozoaires. Archiv, de Bio- 

 logie, T. III. p. 1—49. pi. I— III. 



1881. Metehnikoff, E., Untersuchungen über Orthonectiden. Zeitschr. f. 

 -wiss. Zool. 35. Bd. 1881. p. 282—303. Taf. XV. 



1876. Van Beneden, E., Recherches sur les Dicyémides survivants actuels 

 d'un embranchement des Mésozoaires. Extrait des Bull. del'Acad. Roy. de Belgique, 

 2. sér. T. 41. No. 6, T. 42. No. 7. 1876. pi. I— III. 



1882. Van Beneden, E., Contributions à l'histoire des Dicyémides. Archiv, 

 de Biologie, T. III, p. 195—228. pi. VII et VIII. 



1897. Wheeler, W. M., [Marine Fauna of San Diego Bay, Cala]. Science 

 N. S. Vol. V. No. 124. p. 775—776. May 14th, 1897. 



1883. Whitman, C. O., A Contribution to the Embryology, Life-history and 

 Classification of the Dicyemids. Mitth. a. d. Zool. Stat, zu Neapel, 4, Bd. 1883. p. 1 

 —89. pi. I— V. 



The Hull Zoological Laboratory, University of Chicago, Dec. 20th, 1898. 



