124 The Ottawa Naturalist. [Jan. 



visceral mass is visible, on the left side. The creature has no 

 mouth or digestive canal, or other organs, excepting the egg- 

 producing gland which consists of ovarian follicles between thin 

 muscular septa, each follicle containing a syncytium or mass of 

 united protoplasmic bodies, showing small deep-staining nuclei 

 (the oogonia) and larger nuclei, which are centres of oocytes. 

 Small vacuoles or spaces are present in each oocyte, but there is 

 no trace of yolk in any of these primitive developing eggs. Egg- 

 shaped bodies, much larger than the young eggs, occur in the 

 ovary and in the ventral part of the sac or mantle cavity. These 

 bodies exhibit a central mass of small cells, with nuclei, and a 

 thin cuticle (like the embryonic cells of the Cypris-larvas de- 

 scribed later) around which is a yellow layer of globules, really 

 yolk, outside of all being an external cuticle. There also occur, 

 in the developing eggs, two or three vacuolated cells, each having 

 a darkly staining nucleus. Mr. Potts could find no trace of 

 spermaries, and he concluded that the species is parthenogenetic, 

 the eggs in the ovary, in his opinion, hatching out embryos 

 resembling the Ostracod, Cypris, and these migrating between 

 the muscular layer and the inner ectoderm of the mantle, break 

 through the latter, and then assume the form and structure of 

 the Cypris stage. Among the Cypris-larvae in the mantle cavity 

 are large cells which may be degenerated ova, probably from the 

 mantle wall, these having dropped into the mantle cavity. Mr. 

 G. W. Smith found that in Sacculina, as Mr. Potts tells us, a few 

 unfertilized eggs remained in the ovary after most of them 

 had reached the mantle cavity; but, in Mycetomorpha, these 

 developing eggs are in an advanced segmented condition, and so 

 uniform in structure as to preclude any suggestion that they 

 have degenerated. 



On the left side of the thin-walled mantle sac is an indenta- 

 tion or bay, where a small round orifice occurs, (Fig. 3 ea) the 

 exit of a duct, which curves round the visceral mass, and exhibits 

 an internal opening or outlet from the mantle cavity. Through 

 this duct some larvae may be expelled, but it is unlikely, the walls 

 being so thin and delicate, and lacking the strong musculature 

 seen in Sacculina and Peltogaster, in which species the larvae 

 are forcibly ejected from the parent. Mr. Potts thinks that the 

 larvae escape in Mycetomorpha through apertures formed by 

 the thinning away of the mantle at certain points. In the two 

 Rhizocephalans, referred to, special colleterial glands secrete 

 tenacious matter to bind the eggs in a mass and attach them to 

 the mantle, and in this new form two disc-like patches occur 

 on the upper (Fig. 3 gl.) and lower surface of the visceral mass, 

 which from their position, etc., appear to correspond to such 

 glands modified, and now secreting yolk-matter and nourishing 



