262 M. R. Leuckart on the Young States of some Annelides. 



a direct continuation of the latter. This appears also, especially 

 as the stomach possesses the same lateral caeca as the oesophagus ; 

 these indeed gradually diminish posteriorly and entirely dis- 

 appear about the second third of the body, but at the same 

 time (with the exception of the first caecum) appear very much 

 longer and more considerable than the corresponding processes 

 of the oesophagus. The glandular layer of the stomach is lost 

 upon the intestine, where it is replaced by a greater development 

 of the muscular membrane. The muscular walls, as in the oeso- 

 phagus, are marked with black pigment spots. 



The preceding description only applies exactly, as has been 

 said, to the most developed specimens of our worms ; the younger 

 ones are not only smaller and furnished with a less number of 

 segments (35 to 50), but are also particularly distinguished by 

 the toothed bristles or spines described byBusch. Where these 

 spines were still most completely retained, I observed in the 

 first place a strong tuft on each side of the first segment of the 

 body, inserted upon the dorsal surface behind the tentacular 

 cirrus (fig. 2), and consisting of three or four, or sometimes only 

 two very large shafts, which were armed with short spine-like 

 teeth, and extended nearly half the length of the body. The 

 other segments bore similar, but very much shorter spines, which 

 were also upon the dorsal surface above the dorsal cirrus (fig. 3), 

 but never more than two together. The length of these spines, 

 on the anterior segments at least, might be about equal to the 

 breadth of the segment to which they belonged, but they gra- 

 dually diminished in length posteriorly, as Busch has already 

 stated. Similar organs were never found between the pedal 

 tubercles. 



It is difficult to suppose that the loss of the spines in the 

 larger specimens is only accidental. For this, the number of the 

 spineless individuals was too large. Moreover the spined spe- 

 cimens universally exhibited the greatest variety in the number 

 of their spines and in the presence of these upon the individual 

 segments. Sometimes the spines of the anterior segment were 

 wanting, whilst the others were still uninjured ; sometimes it was 

 the latter that were absent to a greater or less extent. Occa- 

 sionally specimens were found (like fig. 1) which only possessed 

 a few (two or three) spines on some particular spots of their 

 bodies. 



Under such circumstances I have no hesitation whatever, as 

 indeed has already been observed, in regarding these remarkable 

 appendages as a temporary adornment. But it is probable that 

 these spines do not constitute the only provisional organs of our 

 larvae. The circles and combs of cilia may also doubtless be 

 placed in the same category, for the developed Annelida, as far 



