Dr. F. Miiller on the Development of the Stomapoda. 15 



or "bacilli," with rounded apices and very delicate outlines 

 (PI. II. fig. 3). The three upper of these are about 0-2 mill, 

 in length ; the three lower ones attain only one-third of this 

 length. 



With regard to these " bacilli " on the inner antenna of the 

 Crustacea, I may be permitted to make a slight digression. 

 These structures, to which attention has lately been called 

 amongst the lower Crustacea by more than one writer*, appear 

 to be very generally diffused throughout the class. I have found 

 them in different Copepods, in the larva of Balani and Rhizo- 

 cephala, in young Bopyri, in Tandis and other Isopods, in Ca- 

 prella, in many Gammarini, in Hyperia, Cuma, and Bodotria, 

 and in all stalk-eyed Crustacea which I examined for them. I 

 missed them only in some parasites [Bopyrus, Cymothoa) and 

 Crustacea inhabiting the land {Ligia, Orchestia). Of two spe- 

 cies of the last-named genus found here, they are wanting in the 

 one, whilst the other possesses themf. In their number and 

 arrangement, size, and form, they are subject to great vai'iety. 

 I have found a single bacillus in many Isopoda (PI. II. fig. 15), 

 and in the middle of the antenna in a Copepod (fig. 18) ; a fan 

 of about ten bacilli occurs in the young of Bopyrus (fig. 13). In 

 Isopoda, Caprella, and Amphipoda, one or two usually stand at 

 the apex and on the lower surface of the joints of the flagellum, 

 sometimes on all the joints, sometimes with the exception of the 

 basal one (figs. 14, 17). In Squilla, in which the outer branch 

 of the inner antenna is again divided, I found them to the number 



* Schodlei' saw them, in 1846, in Acanthocercus ; Leydig, in 1851, in 

 Branchipus, and subsequently in Polyphemus and other Daplmidse ; Max 

 Schultze, in 1852, in larvae of Balanus. " The peculiar pod-shaped, stalked 

 appendages" (fig. 12) which I met with, in 1846, on the third and follow- 

 ing joints of the flagellum of the inner antennae of the Spharoma of the 

 Baltic may belong here, notwithstanding the difference of their form. 



t Note by Max Schultze : — The structures under discussion are described 

 more in detail than in the passages known to Fritz Miiller, by De la Yalette 

 in his inaugural dissertation ' De Gamraaro puteano,' 1857, by Leydig, ' Na- 

 turgeschichte der Daphniden,' 1860, pp. 42-46, and most accurately by the 

 same author in the ' Archiv fiir Auat. und Physiol.,' 1860, 'Ueber Geruchs- 

 und Gehororgane der Krebse und Insekten,' p. 281. Leydig, like Fritz 

 Miiller, comes to the conclusion that the structures are, in all probability, 

 organs of smell. It does not appear, however, from Leydig's statements, 

 what is to be regarded as essentially characteristic of the appendages which 

 are to be interpreted as organs of smell ; but, independent of their position 

 on the antennae (in the Crabs on the inner pair), their abundance of nerves 

 and a certain delicacy of the external membrane, the obtuse apices and the 

 ap])earance of an orifice in these, may be regarded provisionally as charac- 

 teristic. According to this, the bristle-like feelers first described by me in 

 larvae of Balanus, as issuing near the eye (Zeitschr. fiir Wiss. Zool. iv. 

 p. 191), and overlooked by later observers, but again met with and classed 

 as organs of smell by Fritz Miiller, would rather be tactile organs. 



