7. Anthozoa (incl. Hydrocorallia). A. Zoantharia. 17 



type of the family Bergidse. The author refers all the numerous specimens 

 from the West Indies, which he has examined, to 3 species of Parazoantfms 

 (catenularis, parasiticus, swiftii). The first of these is identical with the type 

 species of Bergia, which therefore is merged into P. These actinians range 

 from the northern Bermudas and Bahamas to the Lesser Antilles. 



Faurot describes the formation of mesenteries in Sagartia parasitica and 

 Adamsia palliata. After 16 cells have been produced from the egg, the blasto- 

 ineres segment irregularly. A morula is succeeded by an irregular blastula 

 the surface of which is marked by ridges and furrows, perhaps produced by 

 displacement of the cells during delamination (which takes 6 to 8 hours). About 

 16 hours after the commencement of segmentation the endoderm is formed 

 and the ectoderm is ciliated. The stomodffium is formed, not centrally but 

 nearer the ventral side, and at the same time and by the same process the 

 first pair of mesenteries arise. The stomodseum is not, in its earliest stages, 

 a tube but a groove, its inesoglreal portion in section being U-shaped. The 

 interior aspect, i. e., the concave part of this groove, forms the siphonoglyph. 

 This groove seems to be formed by 2 lateral folds which are themselves the 

 rudiments of the first pair of mesenteries. At a lower level these folds are not 

 close together but are found near the middle of the right and left lateral walls. 

 One of them is usually better developed than the other. On tracing them 

 down the embryo they gradually pass to the dorsal side and finally unite 

 there by their free edges. They are therefore oblique to the longitudinal axis 

 of the larva, being ventral in the superior portion and dorsal in the inferior 

 portion. The next-formed mesenteries (2. 2) are confluent at their inferior 

 extremities with the first pair and have almost the same (ventro-dorsal) obli- 

 quity. The third and fourth pairs are also oblique but dorso-ventrally. This 

 obliquity is only shown in the inferior portion of the embryo and disappears 

 during later growth. The first 2 mesenteries (1. 1] are united at their origin 

 by the siphonoglyph, while 2 and 2, 3 and 3, 4 and 4 are united in couples 

 (as shown) by their free edges, so that each couple forms a crescentic struc- 

 ture. Such fusion is occasionally seen in adults (e. g., Halcampa clavus). The 

 different size of the mesenteries is not so much the result of their ages as of 



o 



their different positions with respect to the stomodaeum. The secondary 

 mesenteries are formed, not by a fold of endoderm enclosing a mesoglceal 

 prolongation, but by the formation of a small lacuna in that portion of the 

 rnesoglffia abutting on the endoderm. Later this lacuna becomes larger and 

 causes the formation of a thin crescentic film of mesogloea pushing the endo- 

 derm into the ccelenteron. The new pair of mesenteries is formed by this 

 crescent being broken in the centre. These secondary mesenteries are largest 

 in the dorso-lateral, and smallest in the ventro-lateral exocoels, and this pro- 

 bably holds for the third, fourth and fifth C3 r cles of mesenteries. The origin 

 of the secondary mesenteries is not brought about by that of the secondary 

 tentacles as these have not yet appeared. 



Hazen. working on Sagartia luciae, finds that tentacles regenerate at the 

 oral end of aboral pieces cut at different levels; even on very short pieces. 

 The absence of the pedal disc in a piece does not affect the regeneration 

 of tentacles. The time required for the formation of a new disc is longer 

 than that for new tentacles. A cut in the column or in the oral ring does 

 not cause a growth of tentacles unless, in the latter case, some have been 

 lost. If tentacles have been removed, new ones generally regenerate at the 

 place of injury, but they may be intercalated at intervals around the oral ring. 

 A pedal disc regenerates only at the aboral end of a piece and tentacles only 



Zool. Jahresbericht. 1903. Co"lenterata. d 



