390 



Pro£ E. W. MacBride. 



[Nov. 7, 



The first case has been investigated by Shearer, De Morgan, and Fuchs in a 

 paper just published (11). As I showed in 1899 (10), the larvae of these two 

 species are distinguishable in the later stages of their development by the 

 number and arrangement of the " ciliated epaulettes." These epaulettes are 

 loops of the longitudinal band of ciliated ectoderm common to all Echinoderm 

 larvae which acts as their locomotor organ. These loops, when the larvae are 

 about two weeks old, become cut off from the rest of the band and form 

 four horizontally-placed crescents of ciliated ectoderm arranged in a circle 

 round the body of the larva, and in the later stages of development the 

 main work of locomotion is thrown upon them. In the larva of Echinus 

 miliaria, a bright patch of green pigment is formed posterior to each 

 epaulette ; of this pigment there is no trace whatever to be found in the 

 larva of Echinus csculentus. On the other hand, in the larva of Echinus 

 csculentus', when it is about three weeks old, an additional pair of ciliated 

 epaulettes is formed, which are situated nearer the aboral pole of the larva. 

 No trace of these extra epaulettes is to be found in the larva of Echinus 

 miliaris. Finally, in the larva of Echinus csculentus, when it is about four 

 weeks old, a pedicellaria makes its appearance at the aboral pole ; no trace 

 of this pedicellaria is to be found in the larva of Echinus miliaris, though in 

 both larvae lateral pedicellariae are developed. 



Now, Shearer, De Morgan, and Fuchs find that the hybrid larva, with 

 respect to the three characters just enumerated, viz., epaulettes, pigment, and 

 pedicellariae, is always purely maternal, whether the male parent be Echinus 

 miliaris or Echinus csculentus. In fact, the larvae have the character they 

 should have had if the eggs from which they took their origin had been 

 normally fertilised. This result is quite startling, but, as the experiments 

 have been repeated again and again and checked in every possible way, it 

 may be taken as well established. 



Case No. 2, i.e., the cross between Echinus and Echinocardium, had already 

 been included within the scope of Vernon's investigation (13). He crossed 

 the eggs of Echinocardium cor datum with the sperm of Echinus, Strongylo- 

 centrotus, Sphaerechinus, and Arbacia, and obtained in each case about half 

 as many larvae as when the eggs were fertilised with the sperm of the same 

 species. The hybrid larvae were all of the maternal type, but the aboral 

 spike (which will be described later) was considerably shorter in them than 

 in the normal larvae. In most cases, attempts to fertilise the eggs of other 

 wenera with Echinocardium sperm were entirely unsuccessful, but in one 

 case, when the eggs of Echinus were used, one-third of them developed and 

 produced larvae of the purely maternal type. 



The experiments, the results of which are recorded in this paper, were 



