GENERATION. 127 



Echinodermata. The first condition of every Echinoderm 

 is the same, an oval, ciliated body, resembling an infusorial 

 animalcule, and without external organs or distinction of 

 parts. Upon this form are developed, at one part, peduncles 

 for its attachment to other bodies, while the rest of the germ 

 increases in size and assumes a star-fish form. The larvse 

 may be divided into two groups: 



(1) The first including the Ophiuridse and Echinidre are 

 somewhat hemispherical bodies, with one edge of their trun- 

 cated side prolonged into a single flat and wide process, which 

 carries the mouth and O3sophagus; while from the oppo- 

 site extremity project rods, four, eight, or more in number, 

 which form the internal skeleton. These larvae have a 

 globular stomach in their hemispherical portion, from which 

 proceeds a short intestine, terminating in a circular anus. 

 They have, moreover, a ciliated fringe, which consists of a 

 ridge covered with large cilia, passing around the mouth and 

 before the arms, completely encircling the body in an oblique 

 manner. The larval form of the Echiuidse is often spoken of 

 as the Pluteus. 



(2) The second group including tho Holothuridse and 

 Asteroids differs from the above in not possessing an in- 

 ternal skeleton. The larvce of the Holothuridse are concavo- 

 convex bean-shaped bodies, with an irregular transverse 

 fissure answering to the hilum of the bean, in which the 

 mouth is placed. The margins of this fissure are ciliated; 

 the anus opens on the ventral surface. Those of the Aste- 

 roidse closely resemble these last, but they have a distinct 

 ciliated circle in front of the mouth; as they increase in size, 

 the anterior part of their body is covered with long processes, 

 which vary according to different forms. The names Auri- 

 cularia and Bipinnaria are often applied to these larvae respec- 

 tively. (Burnett.) Brachiolaria is the larva of Asteracantliion. 



MOLLUSCA. Polyzoa. In addition to a direct egg-develop- 

 ment, the Polyzoa multiply by gemmation. 



Tunicata. Reproduction by budding sometimes occurs, as 

 in the compound Ascidians; but true generation is more 

 frequently recognized. After complete segmentation an ob- 



