EXOGONE GEMMIFERA. 153 



being on the ventral surface, but it afterwards shifts forward to the anterior end. Then 

 the median tentacle appears, afterwards the two lateral and the caudal cirri on each side 

 of the point of attachment. This is the stage subsequent to that which the sole example 

 from St. Andrews had reached (Plate LIX, fig. 5). In front, that is at the distal or 

 free end of the larva, are the three tentacles, the fused palps forming a ventral projection, 

 the pharyngeal region and the proventriculus follow, then a reddish-brown vitelline 

 mass with oleaginous globules, behind which is the intestine and the anus. The whole 

 is enveloped by the vitelline membrane which, he (Viguier) holds, becomes transformed 

 into the cuticle of the larva, as Stossich found in Serpula. The chief features observable 

 before the larva leaves its parent are the appearance of eyes with lenses, tentacular cirri, 

 the more definite outlining of the pharynx (proboscis) with its tooth, and outlining of 

 the proventriculus, as well as the intestine, together with the occurrence of four 

 bristled feet with dorsal and ventral cirri, the dorsal, however, being absent on the 

 second bristled segment, as in the adult. 



Habits. — This form dwells between tide-marks, and seems to differ considerably 

 from the pelagic types. It is sluggish — rolling in the vessel, and appears to be unable 

 to use bristles or feet actively when carrying the embryos. On immersion in spirit the 

 embryos on its ventral surface were thrown off. 



Exogone gemmifera, from Cette, was first described by Alex. Pagenstecher, in 1863, 

 the year before the example from St. Andrews was found. His specimen was 3 mm. 

 long, had thirty -two segments, and bore what he thought were buds from the ninth 

 to the twenty-second bristled segment on the dorsum. Moreover, the dorsal and 

 ventral surfaces of the buds corresponded with those of the parent. They presented 

 head, mouth, "upper lip," four brownish-red eyes, and four bristled feet, and were attached 

 by a posterior pedicle. The csecal digestive canal was brownish-red, and the proboscis 

 had a tooth anteriorly. He notes sac-like' segmental organs between the seventeenth 

 and twenty-ninth segments, and also the early eggs with the tentacles indicated in the 

 embryo. His supposition that the embryos were buds has been fully dealt with by 

 Viguier. 



The larval forms found on this species are very similar to those on Syllides pidliger, 

 Krohn. 



Claparede (" Glanures," 1864) points out that Pagenstecher was wrong, but that in 

 all probability the larvas in this (which he calls a Sylline, Grube) arose from eggs, as in 

 Exogone and Syllides — attached to dorsal cirri (Krohn) — alternately with blanks. 

 Claparede notes that it is a fact that in this and other forms long and short cirri occur 

 alternately. The young are detached from Syllides pulliger when they have six segments, 

 the third segment, however, being devoid of the dorsal cirrus. 



Giard (1890) thinks that this species is identical with E. liefer 'steinii, Claparede, and 

 probably also with the Pdedojphylax claviger of the same author. 



Malaquin mentions that the young on being set free have the larval pharynx and the 

 proventriculus (the so-called dipharyngeal condition), and when they have four setigerous 

 segments the characters are nearly those of the adult. 



Malaquin found in September several mature male buds of thirteen segments of 

 Exogone gemmifera, with swimming-bristles and heads recently formed, with two large 



77 



