1 00 ENTOPROCTA. 



solid cell-mass containing within it a dense network of fine nerve- 

 fibrils (Punkt-substanz), soon becomes detached from the ectoderm. 

 The tentacles arise as outgrowths projecting into the vestibule. 



The voluntary throwing off of the head, and its subsequent regeneration from 

 the end of the peduncle, has also recently been more carefully investigated by 

 Seeliger. Extensive processes of degeneration occur in the "head" before 

 it is separated. The end of the peduncle, after the detachment has taken 

 place, shows the same composition out of two germ -layers which was 

 found in the stolon, and the development of the new " head " actually takes 

 place under exactly the same conditions and by just the same processes as the 

 development of the buds on the stolon. The spontaneous throwing off of the 

 "head" and its regeneration recall the degeneration and new formation of 

 the polypides in the Ectoprocta. 



The budding in Loxosoma takes place, according to Seeliger (No. 13), in 

 just the same way as described above for Pedicellina. Here also an ectodermal 

 imagination yields the common rudiment of the vestibule and the alimentary 

 caiial, while the mesoderm is derived from the immigrating mesenchyme-cells 

 of the parent-animal. As a rule, the young bud projects early as an outgrowth 



om the parent, but there are certain modifications in the manner in which 

 the buds are attached in the different species. While, in Loxosoma singulare, 

 Raja, cochlear, and phascolosomatum, the buds appear attached to the parent 

 by the peduncle, in L. Kefersteinii, according to Nitsche and Claparede,, 

 the attachment to the parent is in the region of the dorsal side of the bud 

 at the boundary between the peduncle and the trunk. The peduncle therefore 

 does not here grow out as a free projection from the body. According to 

 Prouho, the budding in Loxosoma (Cyclatella) annelidicola is at first internal, 

 the young bud developing in an ectodermal depression forming a kind of 

 amniotic cavity. The buds appear to develop in the same way in Loxosoma 

 Raja; this fact led 0. Schmidt to trace back the formation of buds in Loxosoma 

 to a parthenogenetic development. 



General Considerations. 



In treating of the affinities of the Entoprocta, we must start with 

 the free-swimming Pedicellina larva. This larva may, without much 

 difficulty, be traced back to the Troehophore type. The ciliated 

 rings of the Pedicellina larva would then correspond to the pre- oral 

 ciliated ring of the Troehophore, while the region lying behind the 

 ring becomes invaginated to form the vestibule. In such a com- 

 parison, we have to regard the short line extending between the 

 oral and the anal apertures as the ventral median line of the Ento- 

 proctous larva, the correctness of this view being confirmed by the 

 position of the blastopore. 



In comparing the Entoproctous larva with the Troehophore, we have left the 

 apical plate out of consideration. Whether Harmer's view that the dorsal 

 organ. (a-) is the brain of the larva and the equivalent of the apical plate is 

 sufficiently corroborated by the facts to be observed, must be left to the decision 



