94 BULLETIN OF THE 



The Brigula larvse, on the contrary, I have never found in the tow, but 

 they swarm out from stocks gathered in the morning and placed in a 

 glass vessel ; and I can confirm Nitsche's ('G9, p. 9) observation that they 

 settle and begin their metamorphosis within "a few hours" after hatch- 

 ing. One rarely or never finds these larvaj succumbing to the unfavor- 

 able conditions of the aquarium before metamorphosing. From these 

 observations I conclude that the Bugula larva has a very much shorter 

 life than Cyphonautes. Now, since the larva, owing to its shortened life, 

 has no need of functional entoderm, and since entoderm can be of use to 

 the larva only, no part of it going over into the tissues of the primary 

 polypide of the stock (except as food material), functional entoderm is 

 not developed. In other genera, its rudiments have become less and 

 less important in the ontogeny, and, finally, in Phylactolsemata are 

 wholly lost. 



That the entoderm should reach its last stage of degeneration in 

 Phyladolcemata is easily understood when we consider that the larval 

 period is passed in a closed ooecium, from the wall or neck of which it 

 receives nourishment as a parasite does. Moreover, by the delay in the 

 period of hatching, as well as by precocious development of polypides, one 

 at least of the latter is usually functional in the just hatched stock, for 

 there is sometimes found at least one polypide in the newly hatched 

 larva, which is partly extruded, and therefore capable of feeding, and 

 thus of supplying the whole stock with nutriment. Of what advantage 

 to a species could be the development of a functional larval entoderm, 

 which should go to form no part of its adult tissue, provided the larva 

 was contained in a uterus during its early stages, and was provided with 

 the adult digestive organs in a functional condition before leaving the 

 uterus ? 



Those who maintain that the inner layer is to be regarded as entoderm, 

 and are still unwilling to place the Bryozoa among the Coelenterata, must 

 account for the absence of mesodei'm. Korotneff ('89, p. 400) finds de- 

 generating cells in the blastoccel before this is wholly obliterated by the 

 extension of the inner laj-er. These he seems to regard as degenerate 

 mesoderm. According to his view, then, the entoderm gives rise to 

 the muscularis, — for this arises from the inner larval layer, according 



author does not there state wliether stomorljcnm anrl proctorlasnm are formed on 

 the blastoporic side of the larva. He accounts for the existence of an alimentary 

 tract in Cyphonautes by the fact that it undergoes its development disconnected 

 with the parent, while almost all other Bryozoa pass their early stages in the 

 parent or some protecting zooid (ocEcium, ovisac, ovicell). 



