ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 39 



i iff. The history of the hydrocoel is traced, and the formation of the 

 apical plate and oral invagination. The newly emerged club-shaped 

 larva has very lone cilia and a marked heliotropisin. The form known 

 as Tornaria miilleri is the pelagic stage of Bdlanoglossus clavigerus ; it 

 shows no hint of heart or coelome ; it passes into a Tornaria krohnii 

 stage. The first pair of coelomic sacs arise as solid outgrowths on both 

 sides of the posterior gut. An account is given of the structure and 

 development of the apical plate and of the eve. 



Echinoderina. 



Echinus Hybrids.* — H. M. Fuchs made a cross between Echinus 

 esculentus 9 and E. acutus £ , and successfully reared four of the 

 hybrids. Two of them have laid eggs. Some eggs and sperms were 

 obtained, and the fertilized ova yielded healthy larvae (F 2 generation). 

 When a larger number of the F l hybrids have been reared, an examin- 

 ation of the characters of the fully grown urchins should decide whether 

 the fertile intermediate forms found in the sea are hybrids or extreme 

 variants of one of the two species. 



When the ova of E. miliar is were fertilized with the sperm of the 

 Fj hybrid, or when the sperm of E. miliaris was used to fertilize the 

 ova of the F, hvbrid. it was found that E. esculentus characters and 

 E. acutus characters were developed in both crosses. 



The F 2 generation obtained from the E. esculentus and E. acutus 

 hybrids can give no information as to the inheritance of the late larval 

 characters, since the latter are alike in the two species. It is the F 2 

 feneration from hybrids between E. esculentus or E. acutus and E. miliaris 

 that will give this valuable information ; but no forms of this genera- 

 tion have as yet reached maturity. 



Development of Common Starfish. t — J. F. Gemmill has studied 

 the development of Asterias rubens, the common starfish. The spawn- 

 ing season is from the end of April till the beginning of July. Matur- 

 ation is in progress while the eggs are being shed. Segmentation is 

 total and equal, or practically equal ; the blastula wall is a single layer : 

 the gastrula is formed by invagination ; the mesenchyme arises, after 

 gastralation, from the enlarged blind end of the archenteron. 



The gastrula elongates and the blastopore migrates ventralwards ; 

 the stomodaeal pit and circumoral depression forms near the middle of 

 the ventral surface ; the preoral and postoral bands merge at first into 

 an antero-dorsal strongly ciliated area ; these bands are next continuous 

 in the auricularia and then divide in the bipinnaria. The typical larval 

 filiated processes grow out, all relatively long, slender, and freely movable, 

 especially the postero-lateral pair. The brachia have the preoral band 

 continued over them, and have truncated ends bearing six to eight 

 papillae. The sucker is well-marked with usually two papillae on each 

 side of it : the posterior part of the larval body becomes disk-like and 



* Journ. Marine Biol. Assoc, x. (1914) pp. 464-5. 

 t Phil. Trans., Ser. B, ccv. (1914) pp. 213-94 (7 pis.). 



