108 PKOF. ALLMAN ON THE 



and the subventral vessels present a nearly horizontal direction 

 in the greater part of their course, and then bend down in a 

 vertical direction towards the oral edge of the rectangle ; and as 

 the swimming-plates are confined to the horizontal portion, the 

 direction of each series is that which we meet with in the adult. 

 In the larva we can now plainly distinguish an ahoral edge 

 furnished with swimming-plates, an oral, and two lateral edges. 

 On the latter the vertical ends of the subventral vessels run 

 downwards towards the oral edge, while along this edge the 

 horizontal branches of the stomach-vessels continue to extend 

 themselves towards the angle formed by the meeting of the lateral 

 and oral edges. Here they meet the ends of the subventral 

 vessels, and anastomose with them. Each of the subtentacular 

 vessels also extends in an oblique direction, from its origin under 

 a subtentacular rib which never carries at this time more than 

 a single swimming-plate, towards the same angle, Avhere it meets 

 the other vessels and soon enters into the anastomosis. The 

 course of the vessels which characterizes the adult Cestum is 

 thus in all its essential features established. 



The body continues to elongate itself more and more in the 

 form of a baud ; and with the consequent extension of the sub- 

 ventral vessels and their ribs numerous new swimming-plates are 

 developed on the latter, while a few also show themselves on the 

 subtentacular ribs, and the place of communication between the 

 meridional vessels and the horizontal branches of the stomach- 

 vessels moves towards the middle point of the lateral edges. 



In the meantime the tentacle-apparatus has begun gradually 

 to sink towards the mouth ; and its sheath, appearing as a dupli- 

 cation of the dermal layer of the body, extends more and more 

 over the tentacle, and runs on the margin into two furrows — the 

 later tentacle-furrows. The original tentacle-stem with its ac- 

 cessory branches is still visible on the sheath ; but at a later stage 

 there is no longer any trace of it, and its place is taken by a 

 tentacle-stem formed of numerous coalesced filaments, of whose 

 origin from the reserve tentacle Chun believes there can be no 

 doubt. 



Chun also devotes some pages to a description of the post- 

 embryonal development of the Beroidse. Under this, however, 

 he includes many stages which, in the examples examined by 

 myself, were completed before the escape of the animal from the 

 egg. The diflerence may depend on a difference in the species or 



