272 LETTERS FEOM C. DARWIN, ESQ., 



No. 16. 

 (Postal date 12tli, 1853.) 



Down Farnborougli, Kent, 



Feb. 12tli. 



My dear Sir, 



I will begin a summary of what I have been able to 

 make out on Alcippe, imagining you feel interest enough to read 

 my scrawl. You must believe that I express myself positively 

 only for brevity's sake. 



Mouth. — Every part peculiar, not strictly on normal type of 

 Lepadidse ; the rudimentary palpi, however, found only in Anel- 

 asma. I think your view on the row of hairs on labrum being 

 branchial must be given up ; there are thinner but similar hairs 

 on inner opposed tunic of sack, together serving as a fence to 

 prevent anything crawling into sack by the sides of the labrum. 



Cirri. — The organ you have called palpi, or first cirrus, cer- 

 tainly is the latter, and not much more modified than in Anelasma. 

 The thoracic segment supporting this cirrus is confluent with 

 mouth, and forms the prosoma in normal manner. The second 

 (N.B. This is properly the third segment of archetype crusta- 

 cean.) thoracic segment is large and obscure; the third and fourth 

 very distinct. In one monstrous specimen the fourth segment 

 bore an extra cirrus! showing that the segment is true. The 

 fifth segment small, but quite distinct, and bears the pair of cirri 

 nearest the mouth. The sixth segment, equally distinct, bears 

 the middle pair of cirri. The succeeding and outermost articu- 

 lated organs are not cirri, but caudal appendages. The wonderful 

 little cushion on the inner ramus metamorphosed. The caudal 

 appendages are never biramous, and hence have not cushions. 

 It deserves notice that Alepas cornuta has the inner rami of the 

 fifth and sixth pair of cirri (and of no other rami) rudimentary, 

 without muscles, and short. These three pairs of organs in Al- 

 cippe are all in some respects in an embryonic condition. 



Alimentary Canal. — (Esophagus normal; biliary envelope thick 

 and irregular, as in Anelasma; rectum and anus none. I am 



