ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 805 



stalk and an adjacent portion of the stolon form a movable proboscis, 

 at the end of which a mouth-opening eventually appears. After the 

 disruption of the stolon the individualized buds seem to be nourished 

 at the expense of the yolk stored up in their cavities. These cavities, 

 which extend even to the end of the tentacles, may be justly termed 

 gastral cavities. 



The liberated mother bud (B) with 24 tentacles, divided into two 

 daughter-forms (B 1 ) with 12 each. These divide and give rise to two 

 different forms, B 2 and B 2 6. The successive multiplication of the 

 different generations is fully discussed and tabulated, and the three 

 forms are described. 



In regard to the histology, only a few notes are as yet communicated. 



1. The ectoderm is somewhat folded laterally, and still more, 

 inferiorly. Between the elements long drawn out cells were observed, 

 which bore a transparent hair projecting above the level of the ecto- 

 derm. These may be reasonably regarded as sensory cells. On both 

 sides of the mouth, where the proboscis passes into the main stem, 

 two round masses of cells are seen. They consist of elements larger 

 than the ordinary ectoderm cells, and may be regarded as ganglia. 

 The presence of nerves was not demonstrated. After two or three 

 days' free life the Polypodium acquires a light green colour, due to the 

 presence of pigment-granules, suspended in the protoplasm of the 

 ectoderm cells. 



2. The endoderm exhibits a swelling at the aboral end of the 

 body. In the region of the proboscis, also, a small annular fold pro- 

 jects freely into the inner space, representing perhaps a primitive 

 funnel-shaped oesophagus. At the oral opening the endoderm passes 

 directly into continuity with the ectoderm. The cells exhibit con- 

 tractile root-processes. The ectoderm cells occasionally unite, 

 obliterating the lumen in the tentacles and also in the large internal 

 spaces in the generations B and B 1 . 



3. The mesoderm is represented by the slight muscular sheath 

 of spindle-shaped cells, and is best developed in the proboscis and at 

 the origin of the tentacles. At the transverse aboral furrow, on the 

 other hand, it is rudimentary. This corresponds with the creature's 

 habit of sitting and moving on its tentacles. 



In a postscript, Dr. Ussow describes a younger larval form which 

 had not yet reached the stolon stage. It resembled a non-ciliated 

 planula, with a large central cavity. He regards Polypodium as a 

 hydroid organism, with a motile " trophosome " (B) passing through 

 various asexual generations before attaining the sexual (possibly 

 medusoid !) form. The planula of the latter migrates into the ovum of 

 Acipenser, and gradually developes into the stolon with primary and 

 secondary buds. 



Relation between the Skeleton and the Tissues in Madrepores.* — 

 Herr G. v. Koch has, by clear definitions and diagrams, done much 

 to facilitate the understanding and discussion of Madrepore structure. 

 In the skeleton the following main portions are to be distinguished. 



* Morphol. Jahrb., xii. (1886) pp. 154-60 (1 pi.). 



