MUSEUM OF COMPARATIVE ZOOLOGY. 137 



especial stalk, and not separated from the taster, as in H. rvhrxim. The 

 bracts are small, and so transparent that at first sight one is inclined to 

 doubt their existence in Agalmopsis picta, while in Ilalistemma they are 

 large and conspicuous. This feature effects very considerably the rela- 

 tive forms of the two Jelly-fishes. 



All along the necto-stem and polyp-stem of Agalmopsis picta^ more 

 especially, however, upon the former, there are to be found in the ecto- 

 derm, as Claus has already mentioned, bright crimson pigment spots 

 more clearly marked than is generally the case with similar spots on the 

 stem of other Siphonophores. Two of these pigment spots, together 

 with a finger-like process near them, also exist on the young nectocalyces. 

 In very young swimming-bells there are three of these pigment spots. 

 They occupy a position similar to that of the pigment spots of other 

 hydroid Medus£e, at the junction of the lateral and superior * tubes with 

 the circumvelar vessel. There are very interesting highly refractile red 

 spots of a problematical function covering the bracts in Agalma Sarsii 

 and Agalma clavatum. (PI. I. fig. 2.) These bracts, from the place of 

 attachment and the twisting of the stem, form a well-marked spiral 

 around the polyp stem of the animal. The spots on each side of a cen- 

 tral line are arranged on every scale in irregular rows, extending longi- 

 tudinally across the bract, each pigment spot being enclosed in a cell. 

 These peculiar pigment spots of the covering scales, represented remotely 

 also in some genera, as in Apolemia (PI. I. fig. 1), by elevations com- 

 posed of clusters of cells on the surface of the bract, are the most ap- 

 parent structures in the transparent bract of A. Sarsii, since with that 

 exception there is hardly any coloration in the covering scale. In A. 

 clavatum, the sexually mature young of J.. Sarsii, only four rows of these 

 pigment spots occur, as Leuckart has shown. When the bracts which 

 bear these paralleled rows of spots are detached from the axis, their 

 color changes to a yellow, and a fluid of the same color exudes into the 

 surrounding water. I have not been able to find any mention of this 

 rupture of the cell wall and discharge of a yellow fluid when the bract 

 is detached, in the descriptions by other naturalists. I think these 

 scale cells belong to the ectodermic layer. 



* A nomenclature of the different spheromeres of the nectocalyx of a Siphonophore 

 would simplify a description of the bell. As paired chymiferous tubes opposite each 

 other have resemblances in their course from their relation to a plane passing through 

 the dorsal and ventral line of the stem, they may be called lateral tubes, and the 

 respective sections of the bell in which they lie, lateral spheromeres. The remaining 

 spheromeres, according to their position in relation to a float, where such exists, may 

 be called the superior, or the inferior, corresponding with a proximal and a distal. 



