SYXAPTA VIVIPARA. 57 



to the skin, just behind the circle of tentacles. When placed in aquaria, this 

 Synapta does not break up by muscular contractions, like S. inhaercms, nor does it 

 ordinarily eviscerate like many holothurians, but after crawling about restlessly for a 

 while, it stretches out on the bottom and dies, almost without the contraction of a muscle. 

 In a few cases, evisceration at the mouth took place, when they were thrown into a killing 

 agent. 



Breeding goes on all thiough the spring and summer ; and there is no evidence to 

 sliow that it does not go on all the year round. My earliest specimens, collected April 30 

 contained many well-developed young, and up to the end of July in nil the specimens 

 obtained, young were found, while Ludwig's specimen from Abrolhos was collected in 

 September and contained very young embryos. The number of young in the body- 

 cavity of a single adult varies greatly, depending more or less on the size of the individ- 

 ual. Specimens not over a centimeter long may contain a few, while some very large 

 ones have scores. The largest number I have found is 176. It is a curious fact that the 

 young are almost always in two broods ; that is, a certain proportion of them will all 

 have reached a given age, say that of the pentactula, while the i-emainder will be much 

 younger, say about that of the gastrula. When the young are very few, they will all be 

 the same age, while if they are very numerous, they will sometimes show three different 

 stages. This fact seems to indicate that the eggs ripen and pass into the body-cavity in 

 lots of from six to a hundred, and tliat several days elapse before another lot is ripened. 

 Regarding the length of time during which the young remaiu in the body-cavity, it is 

 impossible to make even an estimate. Animals kept in aquaria frequently gave birth to 

 young only five mm. long, and it was not usual to find much larger specimens in the adults 

 examined, but sometimes a young one, fifteen or twenty mm. long, witli all the charac- 

 ters of the adult, would be found still inside its mother. Observations made on the living 

 animals showed that birth occurs normally at the posterior end of the body, apparently 

 through the anus. Investigation showed that this was accomplished by a rupture of the 

 body-wall, which may be through the skin some little distance from the anus (Fig. 29), 

 or, as seems to be more generally tJie case, through the wall of the rectum close to the 

 point where it joins the external body-wall, the young passing out through the anal 

 opening. It may be that the openings in the wall of the rectum (Figs. 30 and 31), to be 

 described later, are concerned in the birth of the young, but they seem to be too small to 

 be of any service in this connection, except possibly as starting points for the rupture of 

 the rectum wall. Under abnormal conditions, I found by experiment, rupture of the 

 body-wall and consequent birth of the young may occur at other points than near the anus. 



