1913] The Ottawa Naturalist. 125 



the growing ovary. This view is supported by the fact that they 

 were in functional activity though the eggs had just been 

 extruded, and the new series of eggs were in a very early stage. 



As already stated, the eggs give origin to embryos which 

 develop into active little crustaceans exactly like free-swimming 

 Ostracods or water fleas (Cypridas), possessing a transparent 

 bivalve shell and numerous paired limbs, and crowding the 

 capacious mantle cavitv, until they finally find their way 

 into the external water. 



Sylon, a Rhizocephalan, parasitic on shrimps, is known to 

 reproduce parthenogenetically, and the same doubtless applies 

 to Mycetomorpha, as Mr. Potts found no trace of any male organs. 



Mycetomorpha lives upon the juices of its host which are 

 sucked in by the short branches of the root-system (Fig. 4 rs) 

 and carried by a hollow space or lacuna into the short oblique 

 peduncle (Fig. 4 p.) or neck of attachment to the shrimp, this 

 neck being as usual strengthened by a ring of hard chitin, from 

 which a median spike projects forward. (Fig, 2 sp.) The upper 

 branching part or root-system of the peduncle (Fig. 4rs) appears 

 like a matted strip of short branches given off laterally along the 

 under side of the great ventral nerve cord of the shrimp, these 

 terminating in the ventral muscles. The root-system does not 

 penetrate the host extensivelv, like Sacculina, but extends only 

 about a segment and a half of the body in front of the peduncle 

 and less than a segment behind the peduncle. 



Mycetomorpha is a most interesting addition to the marine 

 fauna of Canada. Like other Rhizocephalans it is, when adult, 

 a most degenerate animal, with its rounded shapeless body 

 destitute of limbs, sense organs, mouth and digestive canal, 

 gills, heart or blood-vessels. Clinging tightly to its host by its 

 peduncle with branching extensions, it sucks the nutrient juices, 

 and devotes its sluggish energies to producing eggs, but in the 

 absence of a male, these are parthenogenetic, and they give 

 birth to embryos, which skip some of the larval stages of other 

 Cirripedes, and appear in the mantle or brood cavity as active 

 swimming Cypris-larvas, and seem to then burst through the 

 skin of the parent to wander about in the open waters of the sea. 



Carl Claus said of the Crustacea, as a whole, that their 

 development from the egg is " almost never direct, for it is rarely 

 that the young, after hatching out, possess the form which they 

 will have when adult. Almost always there is a complicated 

 metamorphosis, and when they are destined later to live the life 

 of parasites, the metamorphosis is regressive." Mycetomorpha, 

 in its young stages, could hardly be more unlike its adult form, 

 and in its development and mode of life it is a remarkable 

 illustration of degenerative evolution or regressive development. 



