EFFECTS ON THE HIGHER INVERTEBRATES 



37 



In addition to the effect upon the reproductive system, the general process 

 of reduction in Hydra fusca during inanition has been described in detail by 

 Schultz ('06). During the first week there is noted (except at low temperatures) 

 a remarkable elongation, both body and tentacles forming thread-like extensions 

 often reaching ten times the normal length. In the following weeks (Fig. 7, 

 a-d) the animals gradually retract and become smaller, resulting in very small 

 hydras (reduced to l - normal length or less), but of normal body form. The 

 tentacles become shortened, with swollen extremities; finally they disappear. 

 The body, deprived of tentacles, gradually becomes pear-shaped and later 

 spherical, the oral aperture closed and obliterated. Finally there results a 

 spherical planula of ectoderm and endoderm, resembling the embryonal form 

 (Figs. 8 to 11). Thus involution apparently reverses the processes of embryonic 

 development in Hydra. 



The histological changes in the tentacles of Hydra during reduction are not 

 very striking. Apparently the loss of cells is chiefly at the tips, where degener- 

 ating cells are frequently seen. 



Nucleus 



Nuclei 



Spermatogonia 



^1 w>xVacuole 



Syncytium x^T^^Hf 



Inclusions^^--^ 





Fig. 10. — Ectoderm cells from starving Hydra fusca. Highly magnified. The cells 

 are separated by large interstitial spaces. The cytoplasm is scanty; the nuclei relatively 

 large. A group of the persistent sex-cells (spermatogonia) is shown. (After Schultz '06.) 



Fig. 11. — Entoderm cells from starving Hydra fusca. (After Schultz '06.) Highly 

 magnified. The cells have fused into an irregular syncytium, containing vacuoles, pigment 

 granules and inclusions. The free surfaces of the cells show irregular processes. 



In the body ectoderm (Fig. 10), there is great variation in the resistance 

 of different cells. The epithelium-muscle cells remain flatly extended, with 

 progressive loss of plasma until the nucleus is barely covered. The cytoplasm 

 usually becomes vacuolated. The mematoblasts disappear entirely. Other 

 cells, however, may retain much cytoplasm, sometimes with gigantic nuclei. 

 The gland cells of the foot remain apparently unchanged. The development of 

 the testes (as above mentioned, Fig. 10) proceeds in spite of inanition, "Oder 

 richtiger gerade infolge des Hungers." " Je mehr das betreffende Tier reduziert 

 war, desto weiter war meistens die Reife der Testikel geschritten. Auch 

 wimmelten meine Aquarien, wo ich die hungernde Tiere hielt, bald von Sperma- 

 tozoen. Doch wachsen die Testikel nie zu jenen mammaformigen Gebilden, 

 wie sie gewohnlich bei Hydra fusca erscheinen. Sie blieben weit kleiner und 

 bildeten nur geringere Anhaufung unter dem Ectoderm. Eine Reifung der 

 Ovarien beobachtete ich nie." 



Of the entoderm in Hydra, the so-called gland cells show no morphological 

 changes, although they decrease in number. The intestinal epithelium, how- 



