52 SUMMARY OF CURRENT RESEARCHES RELATING TO 



^ 



or externally to the surface of the body of the parent. The Ophiu 

 roidea are examples of the latter, as are the Echinoidea and the 

 Asteroidea of the former of these two arrangements. 



The simplest cases seem to be presented by E. sanguinolenttis and 

 A. Muelleri; here the arms of the starfish form a brood-pouch. In 

 Goniocidaris canaliculata the ova are found in the anal area, where 

 they are protected by the neighbouring spines. The same is the case 

 with Gidaris nutrix. Leptychaster Kerguelensis has the body covered by 

 paxillfe, the calcareous rods of which form a covering for cavities in 

 which the ova undergo their further development. Eemiaster caver- 

 nosus is well known for the great depth of its posterior ambulacral 

 grooves, in which the ova, covered by the marginal spines, lie pro- 

 tected. In the viviparous Ophiurids the ova are developed in enlarged 

 bursfe, which open into the genital slits ; these may be of an oval 

 form and have their walls strengthened by calcareous rods. 



It is clear that in animals provided with arrangements of this kind, 

 the differences between the males and females must be such as to enable 

 us to speak with a good deal of confidence as to the sex of the 

 specimen in our hands. 



The female of Gidaris memhranipora has a flatter test, and the 

 abactinal area is deeper and larger. The genital plates have a deep 

 oval notch, which extends to the middle of the plate. "It is clear 

 that by this arrangement the extrusion of ova, as much as 2 mm. in 

 diameter, is considerably explained." The author next turns to the 

 better known case of Eemiaster cavernosus, and then passes to the con- 

 sideration of the Holothuroid Gladodadyla crocea, and Psolus ephippiger. 

 In the former the female carries the young on the sucking feet of the 

 dorsal ambulacra, which are considerably shorter than those of the 

 ventral. 



The female, then, in all these cases has secondary sexual characters, 

 and they are always associated with the care of the young. It now 

 remains to be seen whether differences ever obtain which are not due 

 to this cause. Two examples are known to Professor Studer. In 

 Oreaster iurritus he has found two varieties which differ in colour, and 

 the more or less dome-shaped form of the disk. With this difference 

 was associated the presence in one of spermatozoa, and in the other of 

 ova. A somewhat similar case is that of a new species of Ophiothnx 

 (0. Peter si) from the West Coast of Africa. j 



Coelenterata. 

 Diverse Nervous Susceptibilities of Lower Organisms.*— Two 

 animals belonging to the same class, of comparatively simple structure, 

 and therefore exhibiting morphological differences which to us seem 

 trifling, may nevertheless display very diverse reactions when exposed 

 to similar abnormal conditions imposed on them in the course of physio- 

 logical experiments. In our attempt to explain the occult vital powers 

 thus revealed, we are debarred from an appeal to the apparently corre- 

 sponding diversities sometimes encountered in the case of the much 

 * Krukenberg's * Vergleichend-physiologische Studien,' Part 3 (1880) 

 pp. 1-22 (3 figs.)" 



